FLORIDA A&M UNIVERSITY — FLORIDA STATE UNIVERSITY

COLLEGE OF ENGINEERING

CONCRETE DESIGN AND TESTING

(according to ASTM C 39, 79, 143, 173, 192, 496 and ACI 211.1)

By

HUDSON LARSON, MICHAEL MOORHEAD, MELISSA PENNINGTON, AND

HEATHER VANASSCHE

A6

A Laboratory Report submitted to theDepartment of Civil and Environmental Engineering

in partial fulfillment of therequirements for the Civil Materials Laboratory

Submitted:April 21, 2014

TABLE OF CONTENTS

List of Tables 5

List of Figures 6

1 Introduction 7

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.2 Problem Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.3 Research Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.4 Research Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.5 Chapter Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2 Background 8

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Mix Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3 Water to Cement Ratio . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.4 Compressive Strength Design . . . . . . . . . . . . . . . . . . . . . . 9

3 Experimental Program 10

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Experimental Methodology . . . . . . . . . . . . . . . . . . . . . . . 10

3.2.1 Air Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2.2 Compressive Stress . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2.3 Flexural Testing . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2.4 Elastic Modulus . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.2.5 Poisson’s Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.3 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.3.1 Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3.2 Fine Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3.3 Coarse Aggregates . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3.4 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.4 Mixing and Processing . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.5 Specimen Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.6 Test Devices and Equipment . . . . . . . . . . . . . . . . . . . . . . 14

2

3.6.1 ASTM C 192 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.6.2 ASTM C 173 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.6.3 ASTM C 143 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.6.4 ASTM C 469 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.6.5 ASTM C 78 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.6.6 ASTM C 496 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.6.7 ASTM C 39 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.7 Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.7.1 ASTM C 173 . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.7.2 ASTM C 143 . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.7.3 ASTM C 469 . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.7.4 ASTM C 78 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.7.5 ASTM C 496 . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.7.6 ASTM C 39 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4 Experimental Results 18

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.2 Results - Mix Designs . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.3 Results - Fresh Properties Testing . . . . . . . . . . . . . . . . . . . 18

4.3.1 Slump Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.3.2 Air Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.4 Results -Destructive Testing . . . . . . . . . . . . . . . . . . . . . . . 19

4.4.1 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . 19

4.4.2 Tensile Strength . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.4.3 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.5 Results- Non Destructive Testing . . . . . . . . . . . . . . . . . . . . 21

5 Analysis 21

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.2 Fresh Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.2.1 Slump Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.2.2 Air Content Test . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.3 7 Day and 28 Day Test Destructive Testing . . . . . . . . . . . . . . 24

5.3.1 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . 24

Mix A-1 Compressive Strength . . . . . . . . . . . . . . . . . 26

Mix A-2 Compressive Strength . . . . . . . . . . . . . . . . . 26

Mix B-1 Compressive Strength . . . . . . . . . . . . . . . . . 27

Mix B-2 Compressive Strength . . . . . . . . . . . . . . . . . 27

3

5.3.2 Tensile Strength . . . . . . . . . . . . . . . . . . . . . . . . . 27

Mix A-1 Tensile Strength . . . . . . . . . . . . . . . . . . . . 29

Mix A-2 Tensile Strength . . . . . . . . . . . . . . . . . . . . 29

Mix B-1 Tensile Strength . . . . . . . . . . . . . . . . . . . . 29

Mix B-2 Tensile Strength . . . . . . . . . . . . . . . . . . . . 30

5.3.3 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . 30

Mix A-1 Flexural Strength . . . . . . . . . . . . . . . . . . . 31

Mix A-2 Flexural Strength . . . . . . . . . . . . . . . . . . . 31

Mix B-1 Flexural Strength . . . . . . . . . . . . . . . . . . . 31

Mix B-2 Flexural Strength . . . . . . . . . . . . . . . . . . . 32

5.4 Non-Destructive Concrete Testing . . . . . . . . . . . . . . . . . . . 32

5.4.1 Stress vs Strain . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.4.2 Poisson’s Ratio and Modulus Of Elasticity . . . . . . . . . . . 33

Mix A-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Mix A-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Mix B-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Mix B-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

6 Discussion 34

7 Concluding Remarks 36

7.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Bibliography 37

4

LIST OF TABLES

2.1 Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.1 Concrete Mix Designs . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.2 Slump Test Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.3 Air Content Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4.4 7 Day and 28 Day Compressive Testing Data . . . . . . . . . . . . . 20

4.5 7 Day and 28 Day Tensile Testing Data . . . . . . . . . . . . . . . . 20

4.6 7 Day and 28 Day Flexural Testing Data . . . . . . . . . . . . . . . . 21

4.7 Modulus of Elasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.1 Modulus of Elasticity and Poisson’s Ratio . . . . . . . . . . . . . . . 33

6.1 Compressive Design Strength . . . . . . . . . . . . . . . . . . . . . . 35

5

LIST OF FIGURES

5.1 Comparison of Water to Cement Ratio and Slump Test . . . . . . . 22

5.2 Comparing Average Air Content per Mix (%) . . . . . . . . . . . . . 23

5.3 Progression of Compressive Strengths . . . . . . . . . . . . . . . . . 24

5.4 7-Day and 28-Day Comparative Compressive Testing . . . . . . . . . 25

5.5 Compressive Strength and Water Content . . . . . . . . . . . . . . . 26

5.6 Progression of Tensile Strengths . . . . . . . . . . . . . . . . . . . . . 28

5.7 Progression of Flexural Strengths . . . . . . . . . . . . . . . . . . . . 30

5.8 Stress vs Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

6

ABSTRACT

Portland cement concrete is one of the most widely used materials in structuralengineering and building construction. One of the main reasons for its popularityis its adaptability; concrete can be adapted to fit in almost any environment. Con-crete mixtures can employ admixtures, or supplements, that change the chemicalmakeup, and thus durability of the concrete mixture. However, the concrete’s waterto cement ratio will have the largest effect on its overall strength. This experimentexamined how a concrete’s water to cement ratio varied its fresh, strength, and elas-tic properties. In the experiment, four batches of concrete were mixed with varyingwater to cement ratios. The batches were the tested for compressive, flexural, andtensile strength at seven, fourteen, and twenty-eight (28) days after mixing. Elastictesting, or testing for the maximum amount of loading the concrete can take beforeit permanently deforms, occurred thirty-five (35) days after the concrete was mixedand poured. These tests employed standardized test methods as laid out in theAmerican Society for Testing and Materials guidelines ASTM C 39, 79, 143, 173,192, and 496. These methods allowed for comparison to be made between the mixes,since the test methods used to examine the mixes remained constant throughout theexperiment.

CHAPTER 1: INTRODUCTION

1.1 Introduction

The strength properties of concrete, in this case Portland Cement Concrete, areone of the most important factors in concrete mix designs. These properties areprimarily dictated by the water to cement ratio, or the amount of water in theconcrete mix compared of the amount of cement in the concrete mix (Cemex, 2013).This research focused itself on determining what effects the water to cement rationhad on strength and ductility properties.

1.2 Problem Statement

This research focused on the relationship between the water to cement ratio andmaterial properties, specifically the strength and ductility properties. The researchfocused itself around the hypothesis, and widely accepted idea that, a lower water tocement ratio should increase strength, yielding a concrete capable of withstandinglarger loading before failure.

7

1.3 Research Objective

This research is focused on Portland Cement Concretes that do not employ supple-mentary cementicious materials to increase strength. Supplementary cementiciousmaterials, whether they be fly ash, silica fume, slag, or other natural pozzolans, areused to supplement or replace the Portland Cement, while maintaining a certainstrength. For example one part silica fume could be used to replace three or fourparts of Portland Cement without significant strength loss, if any at all (Kampmann,2015b). This research focused purely on what affect the water to cement ratio hason the concrete’s strength and fresh properties without any supplementary cemen-ticious materials in the mix design.

1.4 Research Scope

The scope of this research is limited because the test methods used to determinestrength properties, ASTM C 39, 78, and 496, fail to account for the test specimen’sgeometry and the size of the contact surface between the concrete test specimenand test device (Kampmann, 2012). Another limitation may be the number ofspecimens tested. For example a seven-day compressive strength test may haveonly tested two specimens from a batch, when the use of four specimens may haveimproved the validity of the compressive strength results, since there would havebeen a higher number of test specimens to analyze.

1.5 Chapter Overview

Chapter 2 examined previous research on the topic which reinforces or makes con-cessions to the ideas tested herein. Chapter 3 showed the process for designingthe Portland Cement Concrete mixes, as well as how the tests (ASTM C 39, 79,143, 173, 192, and 496)were set up and conducted. Chapter 4 contained the rawdata from all the test, which was then analyzed in Chapter 5. From the analysisconducted in Chapter 5, Chapters 6 and 7 explained any possible outliers in thedata which may have led to discrepancies between the data and the hypothesis thatas the water to cement ratio decreased the strength properties increased, and thendrew conclusions about said hypothesis and the raw data, which are presented inbulleted from; respectively.

CHAPTER 2: BACKGROUND

2.1 Introduction

This chapter will analyze previous research in an effort to relate it to the experimentat hand. The purpose of researching previous research was to aid in determininghow not only this particular research should be conducted, but to look for possible

8

pitfalls to avoid in conducting these experiments.

2.2 Mix Designs

While the commonly used standard governing concrete mix designs utilizing hy-draulic cements is given by American Concrete Institute’s document 211.1, otherinstitutions have additional guidelines governing mix design (American ConcreteInstitute, 1991). These additional requirements often vary by state, based on theknown external factors that govern ratios of water content, cements, etc., such assulfate exposure, salt water exposure, concrete usage, etc. (of Minnesota, 2014).

2.3 Water to Cement Ratio

The water to cement ratio is one of the most valuable pieces of knowledge abouta specific mix of concrete. Knowing this information in the field is every bit asimportant as calculating it in the initial design, since it is the first indicator of theconcrete’s quality as it strengthens. The water to cement ratio will have an effecton almost every aspect of the concrete’s material properties, these include but arenot limited to the: slump, strength, and elastic properties. (Nantung, 1998).

2.4 Compressive Strength Design

In the design structural concrete mixes, a factor of safety is generally included toensure the design will not fail if an “accident” happens. These safety factors aregenerally found in the laboratory, and are higher than the design values. Thesevalues are generally withheld from the public, and only design values are given. Forexample, a concrete may be said to be able to withstand a load of 10(lbs), but inactuality can withstand 20(lbs). These additional 10(lbs) act as a safety factor, sinceit is likely someone will “accidentally” load the concrete with 12(lbs). This analogyis similar to the idea behind F ′c and F ′cr values. The F ′c value is the design value towhich will be said to be the maximum permissible load, however in actuality, theconcrete will withstand a higher load of F ′cr. Table 2.1 shows the formulas to usedto derive compressive strengths F ′c and F ′cr. (Kampmann, 2015a).

Table 2.1: Design Considerations

Specified (Design) Required Average (Material)Compressive Strength (F’c) Compressive Strength (F’cr)

(MPa) (psi) (MPa) (psi)

Less than 21 Less than 3000 f’c+7.0 f’c+100021 to 35 3000 to 5000 f’c+8.5 f’c+1200

More than 35 More than 5000 1.1(f’c)+5 1.10(f’c)+700

9

CHAPTER 3: EXPERIMENTAL PROGRAM

3.1 Introduction

This chapter goes into depth of the methodology used throughout the experimentas well as describing the materials and the way they were used in the experiment.The procedure that was used will be explained, along with the preparation of thematerials prior to beginning the experiment.

3.2 Experimental Methodology

During this experiment 4 mixes of concrete were mixed, with each mix making6 small concrete cylinders, 9 large concrete cylinders, and 6 concrete beams thatwere constructed and tested. The water content was varied in each mix to providedifferent results. The concrete was initially tested for its air content in all fourspecimens using the formula in equation 3.2.1. With each mix the water contentvaried so the slump values were measured to provide more accurate data. Thecompressive, flexural, and tensile tests were run and the results were concludedusing the equations in the figures below. If the fracture in the flexural test wasoutside the middle third the formula in equation 3.2.3 was used, but if the fractureoccured within the middle third the formula in equation 3.2.3 was used to calculatethe modulus of rupture. The values that were recorded from test method ASTMC 469 were plugged into the modulus of elasticity formula, seen in equation 3.2.4to achieve the elasticity through concrete compression. From the results of ASTMC 469, Poisson’s ratio could also be calculated using the formula in equation 3.2.5.Only the physical properties were changed in the four specimen mixes, the geometricproperties stayed consistent throughout all the mixes of concrete.

3.2.1 Air Content

The Air Content Test is given section 4.3. This equation is used to determine theconcrete’s air content by subtracting a correction factor from the reading given onthe test device’s meter, and then adding any calibrated cups of water used. If the aircontent was greater than the 9% range of the meter on the test device, the calibratedcups of water that were added were cups of a known volume. Thus from the knownnumber of calibrated cups of water added, the volume of water added is known. Thecups are calibrated specifically for the test device used. This was shown by equation3.2.1.

A = AR − C +W (3.1)

Where:

� A = Air Content (%)

10

� AR = Final Meter Reading (%)

� C = Correction Factor (%)

� W = Number of Calibrated Cups of Water Added to the Meter

3.2.2 Compressive Stress

In the compressive testing, the concrete cylinder was subjected not subject to anynon axial stresses. These pure compressive stresses can then be calculated by equa-tion 3.2.2.

σ =P

A(3.2)

Where:

� σ = Compressive Stress

� P = Applied Force

� A = Area

Note the cylinder was not subject to any bending stresses in the compressive testing.

3.2.3 Flexural Testing

In the flexural testing, two different equations were used to describe the modulus ofrupture. Equation 3.2.3 described the modulus of rupture when fracture occurredoutside the middle third of the span length, but not by more than 5% of the totalspan length.

R =3Pa

bavgd2avg(3.3)

Where:

� R = Modulus of Rupture

� P = Maximum Applied Load

� a = Average Distance Between Lines of Fracture and The Nearest Support

� bavg = Average Specimen Width at Fracture

� davg = Average Specimen Depth at Fracture

Equation 3.2.3 describes the modulus of rupture when the fracture initiates in themiddle third of the span length.

R =PL

bavgd2avg(3.4)

Where:

11

� R = Modulus of Rupture

� P = Maximum Applied Load

� L = Average Specimen Length

� bavg = Average Specimen Width at Fracture

� davg = Average Specimen Depth at Fracture

Note the beam length is neglected in both equations 3.2.3 and 3.2.3 for modulus ofrupture.

3.2.4 Elastic Modulus

The Elastic Modulus for the concrete tested was calculated according to equation3.2.4.

E =S2 − S1

ε− (5 ∗ 10−5)(3.5)

Where:

� E = Chord Modulus of Elasticity

� S1 = Stress Corresponding to Longitudinal Strain

� S2 = Stress Corresponding to 40% of the Ultimate Load

� ε = Longitudinal Strain Caused by Stress S2

3.2.5 Poisson’s Ratio

The Poisson’s Ratio for the concrete tested, or the change in transverse strain overthe change in longitudinal strain, was calculated according to equation 3.2.5.

µ =εt2 − εt1

ε− (5 ∗ 10−5)(3.6)

Where:

� µ = Poisson’s Ratio

� εt1 = Transverse Strain at Midheight of Specimen Produced by Stress S1

� εt2 = Transverse Strain at Midheight of Specimen Produced by Stress S2

� ε = Longitudinal Strain Caused by Stress S2

3.3 Materials

Cement, coarse aggregates, fine aggregates, and water were used in order to makethe Portland cement concrete needed for the experiment. The following subsectionswill go more into depth of the quantities used of each material and the generalproperties of the materials.

12

3.3.1 Cement

According to Merriam-Webster dictionary cement is defined as a a powder of alu-mina, silica, lime, iron oxide, and magnesium oxide burned together in a kiln andfinely pulverized and used as an ingredient of mortar and concrete. In this experi-ment Portland cement was used to make Portland cement concrete. Cement is usedas a binder in concrete that requires a chemical reaction that is activated by theaddition of water. The cement used in the experiment is considered to be hydrauliccement due to the need of water for the hardening process. Cement also served asa filler of the voids left by the aggregates.

3.3.2 Fine Aggregates

A fine aggregate is an aggregate passing the 38(in)(9.5(mm)) sieve. The fine aggre-

gates that were used in the experiment are concrete sand. The more fine aggregatesin the mixture the less cement that will be needed to help fill the air voids in themixture.

3.3.3 Coarse Aggregates

According to Merriam-Webster dictionary a coarse aggregate is defined as the por-tion of the aggregate used in concrete that is larger than about 2

16 (in). Coarseaggregates are used to increase the strength of the concrete and provides morerigidity for the material. Coarse aggregates are a very important aspect of the over-all mixture. The coarse aggregates used in the experiment were lime rock of varioussizes. Without the proper amount of coarse aggregates the final product may besusceptible to failure at low loads. On the other hand, if the mixture were to havean abundance of coarse aggregates the final product may have too many air pocketsand end up being unstable.

3.3.4 Water

The water used in the experiment was potable water out of a hose on the side ofthe FAMU/FSU College of Engineering.

3.4 Mixing and Processing

Cement, fine aggregates, coarse aggregates, and water were added to a concretemixer. The materials were added separately and in controlled increments. Theconcrete mixers walls were initially moistened and then all the excess water wasremoved from the mixer. Before the mixer was turned on some coarse aggregatesand water were added to the mixer. Once the mixer was started the fine aggregates,cement, and water were added to the mixer in increments. The mixer needed tobe held at the proper angle as to not spill the materials on the ground or keep thematerials from mixing properly. Once all the materials were added to the mixer thedrum was rotated for 3 minutes to ensure the proper mix. Then the drum rested for

13

3 minutes and rotated for an additional 2 minutes after the rest period had expired.The mix was then deposited into a damp mixing pan and observed to ensure auniform mixture. Four mixes of concrete were mixed in this experiment. Eachmixture had a different water content and slight changes to the other materials. MixA1 consisted of 111.6(lbs) of cement, 54.9(lbs) of water, 257.5(lbs) of fine aggregates(sand), and 377.8(lbs) of coarse aggregates (limestone). Mix A2 contained 111.6(lbs)of cement, 56.9(lbs) of water, 257.4(lbs) of fine aggregates, and 377.5(lbs) of coarseaggregates. Mix B1 included 112.8(lbs) of cement, 55.3(lbs) of water, 256(lbs) offine aggregates, and 376(lbs) of coarse aggregates. While the final mix of concreteconsisted of 112(lbs) of cement, 52.11(lbs) of water, 257.87(lbs) of fine aggregates,and 378.21(lbs) of coarse aggregates. Once the concrete mixes were properly mixedand deposited into a damp mixing pan they were shoveled into 6 small cylindercontainers, 9 large cylinder containers, and 6 beam containers. As concrete wasbeing added to the cylinders and beams the concrete was being manually roded toprevent too much air being trapped in the mixture. The concrete was placed inthe molds in three layers, each layer being manually rodded a minimal of 25 times.After the rodding the outside of the mold was tapped 10 to 15 times with a malletto furthermore ensure less air bubbles and then the top was leveled.

3.5 Specimen Preparation

The specimens were removed from the molds 24 hours after being mixed and wereplaced in a water bath until the time of testing. The flexural strength specimenswere normally cured and then were immersed in calcium hydroxide saturated water.The flexural test was conducted immediately after removal from moist storage. Ifthe specimens had been left out to dry too long it may have reduced the flexuralstrength. For the splitting tensile strength the specimens had to be tested in amoist condition. For the compressive strength of concrete test the diameters of thespecimens needed to be determined. Once the weight was recorded of each specimenand the diameter was measured liquid sulfur was ladled out of a tub into a mold andthe cylindrical specimens were capped before they were able to be tested in orderto ensure an equal compressive force was placed across the whole specimen. Forthe test method for the static modulus of elasticity and poissons ratio of concrete incompression the specimen was kept moist and the specimens ends were perpendicularto the axis. The surface was observed and assured it was smooth. The specimensdiameter and length were measured before initial testing.

3.6 Test Devices and Equipment

Below all test devices and equipment that were required for the research to beperformed are listed by ASTM test.

14

3.6.1 ASTM C 192

The equipment used to complete the Standard Practice for Making and Curing Con-crete Test Specimens in the Laboratory consisted of molds, tamping rods, mallets,shovels, pails, trowels, straightedge, feeler gauge, scoops, rubber gloves, metal mix-ing bowls, scale, mixing pan, slump apparatus, concrete mixer, and a temperaturemeasuring device.

3.6.2 ASTM C 173

The test devices used in the Standard Test Method for Air Content of Freshly MixedConcrete by the Volumetric method were a funnel, mallet, strike-off bar, tampingrod, syringe, calibrated cup, air meter, watertight cap, meniscus, top section, o-ringseal, and measuring bowl.

3.6.3 ASTM C 143

The equipment used in order to complete Standard Test Method for Slump ofHydraulic-Cement Concrete were a mold that was made of metal so it was notreadily attacked by the cement paste. A cone mold with a base of 8 (in) in diame-ter, a top diameter of 4 (in), handles, and foot pieces. A tamping rod was requiredfor compaction and a scoop to add concrete into the mold.

3.6.4 ASTM C 469

The materials used included a test machine that needed to conform to the require-ments of ASTM E 4 and the head and bearing blocks conformed to the requirementsof ASTM C 39. The gauge length was one half of the specimen height. A compres-someter was used consisting of two yokes with the bottom yoke being attachedrigidly and the top yoke attached at two diametrically opposite points. A pivot rodwas used on one side to connect the two yokes to maintain a constant distance. Todetermine Poisson’s Ratio an extensometer was used to measure the strain and thechange in diameter at the midheight of the specimen.

3.6.5 ASTM C 78

A testing machine was used that provided sufficient continuous loading. The flex-ural test was performed using the third-point loading method. The bearing blocksensured proper force application without eccentricity. The blocks extended entirelyacross the width of the specimen. The support blocks were maintained in a verticalposition.

3.6.6 ASTM C 496

The test machine used in the splitting tensile strength of cylindrical concrete speci-mens was required to provide sufficient capacity and a proper rate of loading. Two

15

1/8(in) thick plywood bearing strips approximately 1(in) wide and equal length tothe specimen.

3.6.7 ASTM C 39

The concrete specimens were compressed by a machine with two hardened steelbearing blocks. The top block was spherically seated to ensure uniform compression.

3.7 Test Procedure

The sections below describe the procedure for each ASTM requirement.

3.7.1 ASTM C 173

According to ASTM C 173 the inside of the measuring bowl was moistened andthen filled with freshly mixed concrete in two layers of equal volume. Each layerwas rodded 25 times and then the outside of the bowl was tapped 10 times with themallet. This aided in releasing any large bubbles leftover in the concrete. The excessconcrete was then removed. The top section was then attached to the measuringbowl. 2.55(L) of hose water was added as well as 0.5(L) of isopropyl alcohol. Watercontinued to be added and the liquid level was adjusted until the bottom of themeniscus reached the zero mark. The watertight cap was then tightened on. Themeter was then rolled rigorously at an angle to release air bubbles. Then an invertedshaking method was used to displace the air. The cap was removed to allow the airto rise and the process was repeated until an accurate reading was achieved.

3.7.2 ASTM C 143

In the slump test the mold needed to be dampened initially and then placed on anonabsorbent surface. The mold was then filled with three layers of concrete witheach layer being rodded around 25 times. The concrete was filled above the mold andthe excess was discarded. The mold was then removed carefully from the concrete.The whole test needed to be completed within two and a half minutes from the startof filling the mold. The slump was measured immediately. The vertical differencebetween the top of the mold and the original center of the concrete top surface.

3.7.3 ASTM C 469

The compressometer was slid around the concrete cylinder with the lower yoke beingfixed to the specimen at three attachment points. Once the pivot rod was in placethe upper yoke was fixed to the specimen at two attachment points. Lastly themiddle yoke was fixed to the specimen at two attachment points. The specimenwas then placed on the lower bearing block of the testing machine with the strainequipment attached. The alignment bars were then removed and the axis of thespecimen was aligned with the center of thrust. Then made contact with specimenwith the spherically seated block. The specimen was loaded to 40 [percent] of the

16

reference strength before recording any data. Once the specimen is placed properlythe specimen was then subjected to the full loading and the data was recorded. Thespecimens were 42-day cylindrical concrete specimens. The load and strain readingswere recorded at two points.

3.7.4 ASTM C 78

For the flexural strength of concrete the specimens’ depths, heights, and lengthswere initially recorded and then the support lines were marked. The beams werethen marked with perpendicular lines on each of the four faces of the beam to assurethat the beam was placed into the test machine properly. The initial load was thenapplied to the specimens and the gaps between the specimen and the load applyingblocks was observed to determine if the gaps were even. The specimens were thenloaded continuously at a constant rate until failure. The peak load was recordedand the appearance of the specimens were recorded. The cross-sectional dimensionswere then determined. This was conducted for the 7-day concrete specimens as wellas the 28-day concrete specimens.

3.7.5 ASTM C 496

The cylindrical concrete specimens conducted in the tensile strength test neededto be placed properly onto the test machine. This was done by placing the speci-men axis properly centered in the longitudinal direction. Plywood strips were thenplaced on the lower bearing bar of the machine. The specimen proceeded to beplaced on the plywood strip and an additional plywood strip was placed on topof the specimen. The specimen was then centered. An initial load was placed onthe specimen and then zeroed before beginning the test. The load was appliedcontinuously and constant until the failure of the specimen and the maximum loadat failure was recorded. The type of failure of each specimen was then recorded.This was conducted for both the 7-day concrete specimens and the 28-day concretespecimens.

3.7.6 ASTM C 39

In the concrete compressive strength test the specimens were placed in the testmachine on the lower bearing block. Then the axis of the specimen was centeredwith the center of the thrust on the top. Once the top surface of the test machinemakes contact with the specimen the load was zeroed. A constant load rate of 35

(psi

s) was applied until failure and the maximum compressive strength was recorded.

The fracture pattern was then observed and recorded. This test was conducted for

17

both the 7-day concrete specimens and the 28-day specimens.

CHAPTER 4: EXPERIMENTAL RESULTS

4.1 Introduction

This chapter presents the data gathered during the research performed throughoutconcrete testing. There are four sections: Section 4.2 lists all materials and theirpresence in each concrete mix, Section 4.3 lists data gathered during the slumptest and air content test, Section 4.4 presents the 7 Day and 28 Day Compressive,Tensile and Flexural testing results and Section 4.5 contained a table that holds thePoisson’s Ratio and Modulus of Elasticity for each mix.

4.2 Results - Mix Designs

Mix designs for each concrete batch were recorded during the research and areshown in 4.1. Each mixture contained cement (Type I/Type II), potable water, sandrepresenting the fine aggregate and lime rock representing the coarse aggregate.

Table 4.1: Concrete Mix Designs

MixLime Rock Portland Cement Sand Water Water to Cement Ratio

(lbs) (lbs) (lbs) (lbs) -

A1 377.8 111.6 257.5 54.9 0.49A2 377.5 111.5 257.7 56.9 0.51B1 376.0 112.8 356.0 55.3 0.49B2 378.2 111.7 661.50 52.1 0.47

Mixes A-1 and B-1 were extremely similar in content with the two water tocement ratios being very congruent. Mix A-2 had the largest amount of wateradded, approximately 2(lbs) more than mixes A-1 and B-1. This severely increasedthe water to cement ratio as shown in the analysis section. Mix B-2 contained amuch lesser amount of water than all other mixes, 3(lbs) less than the requiredamount, which decreased the water to cement ratio.

4.3 Results - Fresh Properties Testing

This section presents tables containing the results of the slump test and air contenttesting performed in the research.

4.3.1 Slump Test

The data gathered during the fresh concrete property testing of the slump valuesfor each mixture is placed in table 4.2.

18

Table 4.2: Slump Test Data

MixSlump Cone Height Height After Removal Slump

(in) (in) (in)

A1 12.00 10.25 1.75A2 12.00 5.25 6.75B1 12.00 9.00 3.00B2 12.00 8.00 4.00

Two outliers are clear in the above table, mixes A-1 and A-2. While mixes B-1and B-2 had a similar slump value of 3 to 4 (in), A-1 had a much lower slump at1.75 (in) and A-2 carried a immense slump value at 7 (in)

4.3.2 Air Content

The data from the air content testing completed on the fresh concrete is listed intable 4.3.

Table 4.3: Air Content Data

MixAverage Air Content

(%)

A1 1.75A2 0.50B1 1.50B2 1.75

Mixes A-1, B-1 and B-2 are similar in air content with an average of 1.75%. MixA-2 was significantly different with a value of .5%.

4.4 Results -Destructive Testing

This section shows the compressive strength, tensile strength and flexural strengthtest results from both 7 Day and 28 Day testing.

4.4.1 Compressive Strength

7 and 28 Day testing results showing the ultimate compressive strength for eachconcrete mix are shown in table 5.3.

19

Table 4.4: 7 Day and 28 Day Compressive Testing Data

7 Or 28 Day IDMass Weight

(lbs)DAVG(in)

LAVG(in)

Load(lbs)

Ultimate Strength(psi)

7Day

A1 AVG 28.6 6.01 12.01 141776.4 4960A2 AVG 28.3 6.03 36.06 82529 2740B1 AVG 28.2 6.09 11.94 120097 4130B2 AVG 28.5 6.00 12.05 128633 4550

28

Day A1 AVG 28.6 5.94 11.97 166258.3 6010

A2 AVG 28.6 6.06 12.12 170550 6030B1 AVG 28.5 6.03 12.01 173648 6140B2 AVG 28.5 6.04 12.02 181281 6410

For the 7 day testing results, all but mix A-2 were within the 4000.00 (psi)range. A-1 was the outlier during 7 day testing with an ultimate strength value of2740(psi). For the 28 day ultimate strength all mixes were a similar range of 6000.00(psi).

4.4.2 Tensile Strength

7 and 28 Day testing results showing the ultimate tensile strength for each concretemix are shown in table 5.6

Table 4.5: 7 Day and 28 Day Tensile Testing Data

7 Or 28 Day IDMass Weight

(lbs)DAVG(in)

LAVG(in)

Load(lbs)

Ultimate Strength(psi)

7Day

A1 AVG 8.5 4.03 8.02 21673 425A2 AVG 8.5 4.02 8.06 15120 295B1 AVG 8.5 4.01 8.00 21982 440B2 AVG 8.6 4.02 8.03 27052 535

28

Day A1 AVG 8.4 4.03 7.99 27020 840

A2 AVG 8.5 4.01 8.08 20153 605B1 AVG 8.6 4.01 8.01 27860 550B2 AVG 8.6 4.01 8.01 33392 660

Mixes A-1, and B-1 were both within the range of 400 (psi) for ultimate tensilestrength at 7 day testing, leaving A-2 and B-2 as the outliers. A-2 is a lower valueof 295 (psi) and mix B-2 is a higher value of 535 (psi). For 28 day testing A-2 andB-2 are similar in the range of 600 (psi) and mixes A-1 and B-1 were the outliersfor the ultimate tensile strength. A-1 was a higher value of 840(psi) and B-1 was alow value of 550 (psi).

4.4.3 Flexural Strength

7 and 28 Day testing results showing the modulus of rupture for each concrete mixare shown in table 5.3

20

Table 4.6: 7 Day and 28 Day Flexural Testing Data

7 Or 28 Day IDMass Weight

(lbs)DAVG(in)

LAVG(in)

Load(lbs)

Modulus Of Rupture(psi)

7Day

A1 AVG 64.6 6.047 6.011 8240 675A2 AVG 63.7 6.02 5.99 6083 505B1 AVG 63.7 5.95 6.04 6553 545B2 AVG 64.9 6.02 6.03 7490 625

28

Day A1 AVG 65.8 6.076 6.065 8190 680

A2 AVG 64.6 6.11 6.08 7590 630B1 AVG 64.6 6.01 6.01 8743 730B4 AVG 64.7 5.98 6.04 9105 760

For the 7 day testing, all mixes’ modulus of rupture are within the range of500-600 (psi). For the 28 day test, all the modulus of rupture values increased fromthe 7 day test and were in the range of 600-700(psi).

4.5 Results- Non Destructive Testing

The table 5.1 below presents the statistical results of the Modulus of Elasticity foreach test.

Table 4.7: Modulus of Elasticity

Mix SpecimenModulus of Elasticity Test 1 Modulus of Elasticity Test 2

106 (psi) 106 (psi)

A1 A1T4 N/A* 5.60A1T3 5.45 5.40

A2 A2T1 5.00 5.20B1 B1T1 4.85 4.85

B1T3 5.05 5.15B2 B2T2 5.40 5.30

B2T7 5.30 5.35

CHAPTER 5: ANALYSIS

5.1 Introduction

In this chapter, an analysis of the water content, air content, slump, compressivestrengths, tensile strengths, and flexural strengths was done. The differences be-tween the results of each of the tests done throughout the entire experiment wasultimately an effect due to a change in the concrete mixture on the first day.

21

5.2 Fresh Properties

The fresh properties that were tested included the slump and air content for theconcrete after it was thoughley mixed. These properties were only tested once permix and their results were analyzed in this section.

5.2.1 Slump Test

The slump test is typically used in concrete testing in order to evaluate the consis-tency of the mixture. The biggest factor in creating this consistency is the watercontent. In most cases, the water content and the slump tend to be directly pro-portional to each other. However, in cases where the mixture is extremely wet orextremely dry the standardized slump test is not able to accurately evaluate theworkability or flow of the mixture. In this experiment, the ASTM C 149 standardwas followed to determine the slump of each of the different design mixtures. Afterthe slump was found, it was compared to the water-to-cement ratio as shown in 5.1.

Since the water-to-cement ratio was changed for mix A-2 and B-2, the slumpvalues should reflect a drastic change. On the same note, since the water-to-cementratio was roughly the same for mix designs A-1 and B-1, the slump values shouldcome out roughly the same.

0.46 0.48 0.5 0.52 0.54

2

4

6

8

Water to Cement Ratio By Mass

Slu

mp

Val

ue

(in

)

Mix A-1Mix A-2Mix B-1Mix B-2

Figure 5.1: Comparison of Water to Cement Ratio and Slump Test

As expected, the slump value for the mix A-2 was drastically higher than allother mix designs since it contained 2 more pounds of water than required in it’sconcrete mixture, thus making its water-to-cement ratio much higher as well. MixA-1 and B-1 also provided reliable results, Since the water-to-cement ratio wasslightly higher for mix B-1 than mix A-1, the slump for B-1 was higher than for mix

22

A-1 while staying relatively similar. However, the slump value given for mix B-2was nowhere near expected. Since the mixture contained three pounds less waterthan required, the slump should have resulted in a value that was drastically lowerthan all other mixes. This incorrect slump value suggests that there was probablyan error during the testing of the slump.

Since slump is typically inversely related to concrete strength the values andrelationships found in 5.1, these values were compared to that of the strength testsin order to verify this trend. From the slump test and water-to-cement ratio valuesalone, the predicted trend of strength from strongest to weakest is: mix B-2, mixB-1, mix A-1, and mix A-2.

5.2.2 Air Content Test

The air content test is important because it provides incite into the future durabilityof the concrete mixture once it has hardened. If the required amount of air is notmet, the possibility of early failure in the concrete is increased. On the other hand,too much air in the concrete mixture may result in lower strength. The reductionof strength based on air content alone is typically a 3 to 5% reduction of strengthfor each 1% of additional air content introduced into the concrete mixture. Thetest method used to evaluate the air content for this experiment was the volumetricmethod standardized by ASTM C 173. Chart 5.2, provides the air content foundin each of the concrete mixtures to the nearest 0.25%. These values were latercompared to the durability found in each concrete mixtures.

Mix A-1 Mix A-2 Mix B-1 Mix B-2

0.5

1

1.5

Figure 5.2: Comparing Average Air Content per Mix (%)

Based on the average percent of air content in each mix shown in 5.2 , mix A-1and B-2 should have very similar durability, mix A-2 should have higher durabilitythan the other mixtures since its air content is so much lower, and mix B-1 should

23

have slightly higher durability than mix A-1 and mix B-2.

5.3 7 Day and 28 Day Test Destructive Testing

This section is labeled destructive testing because the tests were performed untilthe specimen failed. This section analyses the condtions of failure during the com-pressive strength test, tensile strength test, and flexural strength test.

5.3.1 Compressive Strength

The compressive strength is important not only because it aids in understanding justhow much load the concrete created is able to withstand before failure, but becausethe type of failure itself may provide incite in understanding what went wrong in thedesign on the concrete. The test method used to evaluate the compressive strengthof each cylindrical concrete specimen was the standard test method according toASTM C 39. The comparison of compressive strength found in each mix for the 7thday and 28th days was put together and shown in 5.3

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

1,000

2,000

3,000

4,000

5,000

6,000

Day of Test

Com

pre

ssiv

eS

tren

gth

(psi

)

Mix A-1Mix A-2Mix B-1Mix B-2

Figure 5.3: Progression of Compressive Strengths

24

Specific comparison of the 7th and 28th day results of the compressive strengthis shown in 5.4. The amount of change in the strength shown is a good indicatoras to how much the concrete grew in strength initially compared to the increase tothe 28th day. On average, the strength increased slower after the 7th day, with theexception of A-2. The strength grew an disproportionate amount after the 7th day.Most of the strength gained for the design mix A-2 happened after the 7th day.

A1 A2 B1 B20

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

4,954

2,740

4,1314,512

6,011 6,032 6,1426,412

Com

pre

ssiv

eS

tren

gth

(psi

)

7-day testing 28-day testing

Figure 5.4: 7-Day and 28-Day Comparative Compressive Testing

As mentioned before, the water-to-cement ratio and slump relationship shouldhave been a good indicator on the strength of the concrete design mixture. Bycomparing the relationships found in 5.3, it was found that the compressive strengthcame out to have the trend expected. The higher the slump and water-to-cementration, the higher the strength. The only exception was the mix A-2. Since thecompressive strength for mix A-2 tested to be much less than that of the othermixtures, it proves that the slump test must have been done incorrectly. The lowwater content provided a low strength even though the slump test provided aninaccurate slump.

25

0.46 0.47 0.48 0.49 0.5 0.51 0.520

2,000

4,000

6,000

Water-to-Cement Ratio

Com

pre

ssiv

eS

tren

gth

(psi

)

7-Day28-Day

Figure 5.5: Compressive Strength and Water Content

The type of fracture shown when the concrete specimens failed was evenly dis-tributed between type 2 and type three. This indicates that half of the cylindersdid not have well formed cones on both ends, and the other half only have one endwith a well formed cone. Most of the cracking was seen running vertically throughone or both of the ends.

Mix A-1 Compressive Strength

The relationship of mix A-1 shown in 5.3 between 7 day and 28 day is that thecompressive strength continued to increase. However, while the strength increasedalmost linearly to the 7th day test making it the strongest, the strength began toplateaus shortly after the 7th day and ended up being second to last in strength.However, it is sort of odd that it had the highest early strength since it did not havethe highest water-to-cement ratio.

The design mix provided quick early strength but the durability seemed to besacrificed. The overall curve of the compressive strength came out to be relativelyclose to a typical strength test of concrete. The mix plateaued exactly how it shouldand the strength should keep consistent over time with the value found during the28 day test.

Mix A-2 Compressive Strength

The relationship of mix A-2 shown in 5.3 between 7 day and 28 day is that while thecompressive strength increased drastically over between the 7th and 28th day, theoverall strength of the design mix proved to be much lower than that of the othermixes. The design mix proved to create very low early strength with the exchangeof having the strength increase drastically with time. While the 7th day testingstrength fell under the expected results because the water-to-cement-ratio was sohigh the drastic increase in strength for the 28th day of testing was unexpected.The slope of the compressive strength between the 7th and 28th day was almost

26

linear. This unexpected slope is suggestive of a possible error during the testing.The possible reasons for this error were later explained in the discussion section.

Mix B-1 Compressive Strength

The relationship of mix B-1 shown in 5.3 between 7 day and 28 day for compressivetesting is that the cylinder provided expected results for the 7th day test and hada linear increase in strength. The strength continued to increase until the 28th daytest but this increase did not happen linearly. The 7th day test provided a sort ofturning point for the increase in strength. The increase from 7th day to 28th washigh enough to give incite of the possible high durability for the mix. It was a bitunusual for the slopes of mix A-1 and B-1 to not be more similar since they hadalmost exactly the same mix designs. However, the differences in the slopes may beaccounted for in other aspects of the mix, since they were done at separate times,such as compaction into the cylinder molds, temperature before and during curingetc.

Overall, the results and relationship between compressive strength and day oftesting turned out to be somewhat predictable and in line with the results of theslump and air test.

Mix B-2 Compressive Strength

The slope of mix B-2 shown in 5.3 between 7 day and 28 day compressive testinglinearly increased up to the 7th day of testing and then continued to increase buthad a much lower slope. This shows that the 28 day test provided results that wouldbe more accurate for comparison after time. The mix design shows early strengthwhile the durability also seemed to be high. As expected, the water-to-cement-ratioproved to be accurate in predicting that this mix design would show the highestoverall strength, however the strength was not the highest in the 7th day testing.

Overall, the results and relationship between the compressive strength and theday of testing came out mostly ordinary and within the expected range of results.While there was one cylinder that displaced a type 4 failure, this was assumed tobe an outlier.

5.3.2 Tensile Strength

Tensile strength is an important property of concrete because concrete structuresare highly vulnerable to tensile cracking, so the tensile strength test gives goodincite on how much loading may be applied to create failure. Since it is difficult toapply uniaxial tension to concrete specimens, this experiment used an indirect testmethod. The method used to determine the relationship between tensile strengthof the different hardened concrete mix designs and day of testing shown is 5.6 wasthe ”Standard Test Method of Splitting Tensile Strength of Cylindrical ConcreteSpecimens” according to ASTM C 496. The only consideration that must be takenwhen analyzing the results of this method is that the strength relationships givenby the method used for this experiment will contain higher values of tensile strength

27

than the uniaxial tensile strength. With this in mind, the slope of the results shouldbe theoretically the same and can therefore be used for accurate analysis of thespecimen.

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

100

200

300

400

500

600

700

800

900

Day of Test

Ten

sile

Str

engt

h(p

si)

Mix A-2Mix B-1Mix A-1Mix B-2

Figure 5.6: Progression of Tensile Strengths

The tensile strength is typically used as a good indicator as to how well theaggregates were bonded and coated to the cement paste during mixing. Therefore,a low tensile strength may indicate that a certain mix design was not properly mixedor that certain amounts of ingredients were too high or too low for good bondingwithin the mix. The cohesion is a factor of all ingredients but since the water andair were the only differences between mix design, their amounts will be the onesthat mostly determine the cohesion. Concrete with a higher w

c ratio was typicallymore susceptible to cracking and shrinkage. Shrinkage then leads to micro-cracks,which ultimately aided in failure.

28

Mix A-1 Tensile Strength

The increase in tensile strength for mix A-1 as shown in 5.6 was almost linear inslope up to the 7th day test and then the strength continued to increase at a slopethat was slightly lower. The high tensile strength at day 28 of testing indicates thatthe aggregates were probably well coated and the mixture had a very good overallbonding creating very high cohesion. This high cohesion was attributed to the verylow water-to-cement ratio because of the inversely proportional relationship betweenconcrete strength and the water-to-cement ratio. The 7th day testing strength showsthat there was low early strength.

During the trials of this experiment, the failure patterns created were: smoothcut on one end while rough on the other, broken exactly in longitudinal axis withclean breaks with sharp edges, and broken in longitudinal axis at the exact middlewith small amount of cracks.

It was unexpected that the relationships and slopes of the strength vs day oftest for tensile vs compression did not correlate. The tensile strength theoreticallyshould have had a much lower slope after the 7th day testing.

Mix A-2 Tensile Strength

As expected, the slope of the tensile strength shown in 5.6 was practically linear upto the 7th day of testing, however the slope was much higher than expected betweenthe 7th day and 28th day. The slope should have significantly decreased after the7th day of testing. However, even thought the slope is higher than expected, itcorrelates to the slope of the mix during the compressive strength testing at 28days. Another unexpected result was that the strength was not the overall lowest ofall the mixes. Since the water to cement ratio was the highest, the strength resultsshould have reflected this.

During the trials of this experiment, the failure patterns created were: failuresplit through the middle with one half broken in half, failure split completely thoughmiddle, and the failure split completely down the middle while one-third of one halffell off.

Mix B-1 Tensile Strength

As expected, the slope of the tensile strength shown in figure 5.6 was almost linearup until the 7th day of testing, then the slope was significantly decreased after the7th day creating a slope of almost zero when the 28th day test was reached. Thisimplies that the strength for this mix would no longer increase overtime becausemaximum strength had been reached. This is an ordinary and expected result forconcrete.

It is odd that the slope and relationship shown in figure 5.6 does not coincidewith the slope shown in figure 5.3. The slope for mix B-1 in compressive strengthshould have been smaller.

During the trials of this experiment, the failure patterns created were all thesame and consisted of the specimen breaking in exactly two halves.

29

Mix B-2 Tensile Strength

As expected, the slope for tensile strength vs day of test as shown in 5.6 was increas-ing practically linearly up until the 7th day and then the slope dropped significantlyup until the 28th day of testing. At the 28th day the slope was not completely flat sosome increase was still expected but the strength should not increase dramatically.

The compressive and tensile strength slopes for mix B-2 shown in 5.6 and 5.3should have come out more similar. Instead, the slope for the compressive strengthbetween day 7 and 28 was dramatically higher than that of the tensile strength.Because the tensile strength test shown a more normal curve fore concrete testing,it suggests that there may have either been an error in the testing of the compressivestrength of concrete for this particular mix or there was a significant difference duringthe curing or rodding before the experiments were done that made the results comeout so differently.

During the trials of this experiment, the failure patterns created were all thesame and consisted of the specimen breaking in exactly to halves.

5.3.3 Flexural Strength

The flexural strength test is important because it is a measure of how much theconcrete can resist failure in bending. It is typically ten to twenty percent of thecompressive strength. The flexural strength test used for this experiment is basicallyanother way to indirectly determine the tensile strength of the concrete instead ofby uniaxial loading. The method used to determine the relationship between theflexural strength and the day of the test shown in graph 5.7 was the “Standard TestMethod for Flexural Strength of Concrete (Using Simple Beam with Third-PointLoading)” according to ASTM C 78.

0 5 10 15 20 25 300

200

400

600

Day of Test

Fle

xu

ral

Str

engt

h(p

si)

Mix A-2Mix B-1Mix A-1Mix B-2

Figure 5.7: Progression of Flexural Strengths

30

Because the flexural tests were so sensitive to specimen preparation, curing, sur-face moisture, and handling, the resulting relationships between the flexural strengthfound and the day of test was not taken too heavily. Overall, the resulting relation-ships between flexural strength and day of test did not correlate well to the resultsof the tensile or compressive strength tests. This indicates that there was probablymultiple errors during testing.

Mix A-1 Flexural Strength

While the slope for the flexural strength vs the day of test shown in 5.7was positiveand almost linear up to the 7th day of testing, the slope from the 7th day to the28th day varied from positive to negative. The positive slope up to the 7th day wasexpected, it did not correlate with the slope of the tensile strength. The fact thatthe 28 day flexural strength actually decreased was a cause for concern. A negativeslope for strength indicated that the concrete specimen lost strength so there wassome sort of error during the experimentation. Since the flexural test is so sensitiveto the condition of the specimen before the loading begins, there was probably anerror with the specimen before the testing even began. One likely cause of this errorcould have been early drying of the surface of the specimen before testing. Sincethe specimen is never supposed to dry before a flexural test, the specimen wereprobably mistakenly dried before testing causing a much lower strength to result.The location of the failure was the middle third for all three trials.

Mix A-2 Flexural Strength

The relationship between the flexural strength and the day of test was shown in 5.7.The slope of the mix up to the 7th day of testing was high then the slope droppeddown to almost zero as it approached the 28th day of testing. This indicates thatthe flexural strength probably had maxed at the 28th day testing and thereforewould not be increasing any more over time. The 7th day and the 28th day flexuralstrength fell between the 10 to 20 percent range of the compressive load found so theoverall curve seemed to come out normal and predictable. This indicates that therewas a somewhat normal correlation between the compression and flexural results.The location of the flexural failure was at the middle third for all three trials.

Mix B-1 Flexural Strength

The relationship between the flexural strength and the day of test was shown in5.7. The slope of the mix up to the 7th day of testing was positive and produced acurve that was almost linear. The slope of the curve that was produced from 7thday to 28 day, while also being positive, was much smaller in comparison. Whilethe slope should have gone down to almost zero and flattened out, it produced acurve that resulted in a somewhat predictable final value. The 7th day and 28 daysflexural test provided strengths that fell between the 10 to 20 percent range of thecompressive strength tested. The water-to-cement ratio correlated to the flexuralstrength found, this implied that the test for flexural and compression was done

31

correctly and the results provided were, on average, accurate. The location of theflexural failure was at the middle third for all three trials.

Mix B-2 Flexural Strength

The relationship between the flexural strength and the day of test was shown in5.7. The slope of the mix up to the 7th day of testing provided results that fellbetween the typical range of 10 to 20 percent of the compressive strength found.The flexural strength gained up to the 7th day of testing was positive and had analmost linear relationship. The flexural strength, from the 7th day to the 28 dayalso increased but with a slope that was much smaller. The flexural strength foundat day 28 correlated to the water-to-cement ratio in that the water-to-cement ratioprovided a high flexural strength. This correlation indicated that the compressivestrength and flexural strength tests were most likely done correctly and the resultsmay be used as being accurate. The location of the flexural failure for both trialswas at the middle third.

5.4 Non-Destructive Concrete Testing

This test was done in order to determine the static modulus of elasticity and Pois-sion’s ratio in compression for each of the hardened concrete design mixtures. Themodulus of elasticity is also known as Young’s modulus and it is directly propor-tional to the stiffness in the concrete. Since the Modulus of Elasticity of concrete incompression ranges from 2x106 to 6x106 (psi) , the results of this test should havevaried accordingly. This experiment followed the ASTM C469 standard method andthe resulting stress strain relationship per mixture was shown in graph 5.8.

−150−100 −50 0 50 100 150 200 250 300 350 400 450

·10−6

500

1,000

1,500

2,000

Strain ε

Stress σ (psi)

Mix A-1Mix A-2Mix B-1Mix B-2

Figure 5.8: Stress vs Strain

32

Since the compressive strength of the concrete mixtures was also found, theresults of how stiff or elastic the concrete was during the non destructive testingmay be compared to the compressive results to check for accuracy and reliability inresults. While outliers may occur the general results of the two tests should resembleone another. Since this test only applies 40% of the ultimate strength determinedfrom the compressive strength test, it is very important that the concrete does notfail during the test.

5.4.1 Stress vs Strain

As seen in 5.8 , the stress vs strain relationships created were on average predictableand normal. The cylinders did not fail during the experiment which was the expectedresult. The average elastic modulus listed in 5.1 fell within the normal range ofconcrete, this indicates that the compressive strength results were most likely donecorrectly and are therefore accurate.

5.4.2 Poisson’s Ratio and Modulus Of Elasticity

Table 5.1 presents and analysis of the Poisson’s Ratio and Modulus of Elasticity forall mixes except for A-2. Mix A-2 was excluded because the lack of enough testingdata since two out of four tests performed on this mix failed.

Table 5.1: Modulus of Elasticity and Poisson’s Ratio

BatchPoisson’s Ratio Chord Modulus of Elasticity

AverageCoefficient of

VarianceAverage

Coefficient ofVariance

- % 106 (psi) %

B1 0.26 3.45 4.98 3.02A1 0.26 18.63 5.47 1.04B2 0.26 14.86 5.34 0.60

Mix A-1

As seen in 5.8 , the stress vs strain relationships created were on average predictableand normal. The cylinders did not fail during the experiment which was the expectedresult. The average elastic modulus listed in 5.1 fell within the normal range ofconcrete, this indicates that the compressive strength results were most likely donecorrectly and are therefore accurate.

33

Mix A-2

Mix A-2 was the only one to have failed prematurely to the estimated 40% ofultimate strength. The yield point around 1,500 (psi) indicated that the specimenbegan to fail at that point. Since 2 of the 3 cylinders tested resulted in prematurefailure, the results suggest that either the two cylinders were outliers or the ultimateyield from the compressive strength test for this mix was not accurate.

Mix B-1

As seen in 5.8 , this mix provided stress vs strain relationships that were predicted.The yield point was not reached and therefore the experiment did not produce afailure while loading up to 40% of the maximum yield found during the compressivestrength testing. The average Emodulus shown in 5.1 created fell between the typicalrange for concrete, this indicated that the testing for concrete strength was onaverage done correctly and correlated accurately to the non-destructive test. Whilemix designs A-1 and B-1 produced similar results as expected, the E modulus formix B-1 was smaller than mix A-1. This suggested that mix B-1 created cylindersthat were slightly more elastic. Since the design mix for B-1 created a slightlyhigher compressive strength and slightly lower water-to-cement ratio, the Emodulusfor mix B-1 should have been slightly higher than that of the mix design A1.

Mix B-2

As seen in 5.8 , this mix design provided stress vs strain results that were somewhatpredicted. The yield point was not reached during the loading and therefore failuredid not occur. This was expected since the loading only reached up to 40% ofthe maximum ultimate yield found during the compressive strength testing. Inaddition, the elastic modulus that this test created was well within the typicalrange for concrete as shown in 5.1, this furthers that the compressive strength andnon destructive tests were done correctly and produced reasonably accurate results.

CHAPTER 6: DISCUSSION

In this experiment during the initial design and mixing phases, after the theconcrete’s mix proportions were determined, there were changes made to the designby the experiment supervisor. Specifically, for concrete A-2, more water was addedto the mix than initially the mix was designed for. This increased the water tocement ratio, and could account for the high slump of the fresh A-2 concrete. Thisaddition of water had a ripple effect through the strength tests that later occurred.For example, seen in figure 5.3, the 7 Day compressive strength was much lower thanthe other concretes, which did not have their “adjusted” water content adjusted. Itshould be noted, however, that the 28 Day compressive strengths for the concreteswere all similar, which can be expected. As the concretes had longer times to cure,the compressive strengths should converge, since the water to cement ratios were

34

similar; however the concretes with lower water to cement ratios did have highercompressive strengths, as seen in figure 5.5. Again in the tensile testings, the tensilestrength of concrete A-1 was significantly lower than the other concrete mixes when7 Day testing occurred.

In non-destructive testing the Poisson’s ratio for concrete A-2 is almost threetimes higher than the other three concretes, A-1, B-1, and B-2. The coefficient ofvariation for both Poisson’s ratio and chord modulus of elasticity are the highest ofall concrete mixes. The high Poisson’s ratio value may be explained in the coefficientof variation. Since three tests for Poisson’s ratio were conducted the sample sizeof the statistical analysis conducted was so small that the power of the analysisis small. This means had three been more tests, the sample size would have goneup, and theoretical distributed the data in a normal manner, making the statisticalanalysis more powerful.

In the slump testing, the slumps do not necessarily correlate to the water tocement ratios as expected. Concrete A-2 had the highest water content in the andthe highest slump; however, B-2 had the lowest water content, but did not havethe lowest slump. The problems seen in B-2 may have been caused by differencesin the rodding technique, as the mixes were not rodded by the same person. Inaddition, there could have been a difference in the time between the mixing beingcompleted and the slump testing occurring. While the slumps were tested soon afterthe fresh concrete had finished mixing, there was a wait for slump test equipmentto become available since the mixes were poured at roughly the same time. Thissmall wait time could have allowed the concrete to set slightly, which could have inturn lowered the slump value.

Table 6.1: Compressive Design Strength

BatchMeasured Average

Compressive Strength, f ′cr

DesignCompressive Strength, f ′c

(psi) (psi)

A2 6030 5000B1 6140 5000A1 6010 5000B2 6410 5000

The values for f ′c and f ′cr, as shown on 6.1, are design and experimental compres-sive strength values, respectively. The minimum compressive strength f ′c is definedin ASTM C 94 as “The average of any three consecutive strength tests shall be equalto, or greater than, the specified strength, f ′c and when the specified strength is 5000(psi) or less, no individual strength test (average of two cylinder tests) shall be morethan 500 (psi) below the specified strength, f ′c” (ASTM-International, 2004). Thismeans the minimum compressive strength value is inherently lower than the f ′cr

35

values, since the f ′cr values are the experimentally determined value to which thef ′c values are based on. The f ′cr can then be likened to a safety factor. Since theactual compressive strength f ′cr, will be higher than the recommended compressivestrength f ′c, if the concrete is subject accidentally to a load slightly higher thanallowed by the f ′c value (but not exceeding the f ′cr value), the concrete will not fail.In the case of the concretes designed in this experiment, the f ′c value was measuredto bee 5000 (psi) of all mix designs, and none of the individual tests for compressivestrength for the mix designs were below 4500 (psi). This confirms the validity ofthe use of 5000 (psi) as the f ′c for all mix designs.

CHAPTER 7: CONCLUDING REMARKS

7.1 Conclusions

This chapter summarizes the conclusions drawn from the experiments run over thecourse of the research.

� The water to cement ratio is an indicator of strength

� As the water to cement ratio increases, the overall strength decreases. Thiswas most easily seen in figure 5.5

� Slump is generally dictated by the water to cement ratio; this is supported byconcrete mix A-2 which had both the highest water to cement ratio and slumpvalue

� From the slump value, uses for the concrete can be determined according toACI 211.1

– Concretes A-1, B-1, and B-2 have slumps that are allowable in the con-struction of: beams, reinforced walls, and building columns

– Concretes A-1 and B-1 could also be used in: plain footings, caissons,substructure walls, reinforced foundation walls and footings, pavements,slabs, and mass concrete

� All the concretes mixed are suitable for use in thin structures exposed tocontinual wetness, or to frequent freezing or thawing, based on the water tocement ratios; according to ACI 211.1

� All the concretes, with the exception of A-2 could be exposed to moderatelevels of sulfates in soil or water, according to their respective water to cementratios; according to ACI 211.1

36

BIBLIOGRAPHY

American Concrete Institute (1991). Standard Practice for Selecting Proportions forNormal, Heavyweight, and Mass Concrete, (91). Farmington Hills, MI.

ASTM-International (2004). Standard Test Method for Compressive Strength ofCylindrical Concrete Specimens, (C 39/C 39 M). West Conshohocken, PA.

Cemex (2013). “The effects of water additions to concrete: “what’s a little watergoing to hurt?”.” Technical Bulletin 9.1, Cemex USA.

Kampmann, R. (2012). “The influence of the compression interface on the failurebehavior and size effect of concrete,” PhD thesis, The Florida State University.

Kampmann, R. (2015a). “Designing concrete mixtures: Selecting proportions ac-cording to aci 211.1.

Kampmann, R. (2015b). “Supplementary cementicious materials (scm).

Nantung, T. E. (1998). “Determination of water-to-cement ratio in fresh concreteusing microwave oven.” Interiml report, Indiana Department of Transportation.

of Minnesota, S. (2014). “Structural concrete contractor mix design pilot projects.”Technical Bulletin S-1, Minnesota Department of Transportation.

37