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Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

Bantúg (Volume 9) 38

Comprehensive strength of masonry mortar with chalk

powder as admixture

Mujahid A. Dagadas

Aldrin Ray D. Deputado

Monica G. Piang

College of Engineering

Engr. Audrey B. Aba Adviser

Abstract

The study shows the effects of using chalk powder as admixture to the compressive

strength and setting time of the mortar. Different percentages (0%, 5%, 10%, 15%, and

20%) of chalk powder with respect to the weight of cement were added to the mortal

specimen and were tested after 7, 14 and 28 days of curing using a machine available.

As a result, after 28 days curing, the mean compressive strength of mortar specimen

reached 7280 psi, 6600 psi, 6260 psi, 4760 psi and 3280 psi at 0%, 5%, 10%, 15% and

20% respectively. In relation to the setting time of the mortar, the initial and final

setting time delayed as higher percentage of chalk was added in the mix. Using One-

Way ANOVA, the tool showed that there is a significant difference in the compressive

strength of mortar specimen having different percentage of chalk powdered added at

different days of curing. Further, a Tukey-HSD test, a post-hoc test, presented that there

is a significant difference between compressive strengths of mortal having different

percentage of chalk powder. Addition of chalk greater than 5% of the weight of the

cement present deemed to lower down the strength of the mortar. Chalk added at least

5-10% may reach the design strength of the specimen without admixture. Thus, only 5-

10% chalk powder added is reasonable to use as it produces a strength close enough

to the design mix used.

Keywords: Building construction, masonry mortar, chalk powder, admixture,

comprehensive strength

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

39 Bantúg (Volume 9)

INTRODUCTION

Building construction today is a significant part of industrial culture

which is a manifestation of its diversity and complexity and a measure of its

mastery of natural forces that can produce a widely varied built environment to

serve the diverse needs of society (Chang & Swenson, 2012). Construction

industry has been one of the most booming industries in the world. This industry

is mainly an urban based one which is concerned with preparation as well as

construction of real estate properties. The repairing of any existing building or

making certain alterations in the same also comes under construction industry

(Economy Watch, 2010).

Mortar plays an important role in the construction industry, commonly

acting as a bonding element that holds together masonry units, bricks and stones

in structures and buildings (Dhir et.al, 2018). Mortar is made by mixing cement,

lime paste, sand and water proportionally. According to the main applications,

it is divided to masonry mortar and finishing mortar. Building mortar applied to

masonry brick, masonry stone, building block and the like is called masonry

mortar, which takes the function of cementing and transmitting load. Finishing

mortar is also called plastering mortar and is used to plaster the surface of

structures and structural components, with the functions such as protecting the

substrate, satisfying operational requirements and improving artistic appearance.

In the Philippines, most schools are using chalkboard as method of

instruction. Writing using chalk and subsequent cleaning of the chalkboard

generates chalk dusts. Residue of the chalk, commonly called chalk dusts, are

seemed to be of huge amount retained on the chalk ledges of every blackboard.

Since an abundant of chalk dust are present in most schools, a research work

has been undertaken in order to look into the effect of chalk dusts as an admixture

on the compressive strength of mortar and to know if it can be used as an admixture

in the production of mortar. Hence, the researchers hope that this study will

contribute to the field of construction and industry the information that chalk dusts

can affect the compressive strength of mortar.

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

Bantúg (Volume 9) 40

Review of Related Literature

The study of Ahmed on 2010 investigated the use of super plasticizers

as admixtures on concrete significantly improves concrete properties in terms of

workability without increasing water demand; increasing in ultimate strength

gain by significantly reducing water demand without affecting workability.

Super plasticizers admixtures provide improved durability by increasing

ultimate strength and reducing water/cement ratio and likewise save cost of the

reduced cement of about (4.5 – 8.9) % per cubic meter of concrete.

An article about another admixture by Federal Highway Administration of

U.S. Department of Transportation which centered the use of fly ash as an

admixture in Portland Cement Concrete overviews that the used of fly ash as an

admixture for concrete enhances the performance of the concrete. Portland cement

contains about 65 percent lime. Some of this lime becomes free and available during

the hydration process. When fly ash is present with free lime, it reacts chemically

to form additional cementitious materials, improving many of the properties of the

concrete. The many benefits of incorporating fly ash into a PCC have been

demonstrated through extensive research and countless highway and bridge

construction projects. Benefits to concrete vary depending on the type of fly ash,

proportion used, other mix ingredients, mixing procedure, field conditions and

placement. Some of the benefits of fly ash in concrete: higher ultimate strength,

improved workability, reduced bleeding, reduced heat of hydration, reduced

permeability, increased resistance to sulfate attack, increased resistance to alkali-

silica reactivity (ASR), lowered costs, Reduced shrinkage, increased durability.

Many studies of fly ash admixture in concrete conducted also showed results above

and is widely used around the world for different types of construction, in fact

ASTM C618 (Standard Specification for Coal Fly Ash and Raw or Calcined Natural

Pozzolan for Use in Concrete) and ACI 232.2R-03: (Use of Fly Ash in Concrete)

are some of the standard specification for the use of fly ash as admixture in concrete

for different use. The use of super plasticizers and fly ash as admixture greatly

improved the strength of the concrete furthermore reducing the water-cement ratio,

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

41 Bantúg (Volume 9)

heat of hydration and reducing the amount of cement therefore can be used as

cement replacements.

Ivey and Hirsch (1967) investigated the effects of chemical admixtures on

concrete and mortar which centered comparisons between mortar tests and concrete

tests in the areas of compressive strength, shrinkage, and setting time show some

promise for the use of mortar test as indicators of the relative performance between

admixtures. All admixture concretes and mortars tested showed higher 7-28-day

compressive strength than control concretes or mortars when they were allowed to

utilize their characteristic water reduction.

A similar study was conducted by Belyakov and Bannikova (2016) showed

that addition of chemical admixture Relamix T-2 in the amount of 0.6% of cement

mass increases polysterene concrete mix workability. Water reduction decreases

water consumption by 30%, while polysterene concrete durability growth during 28

days achieves 3.7 MPa as compared to durability of reference specimens made

without admixture. It is likely that this fact is due to interaction of admixture-

composing chemical compounds (strength gain accelerating system) with activated

alumina, silica, silicates and calcium sulfide forming part of blast-furnace slag. Use

of Relamix admixture in the amount of 1% and more of cement mass leads to

disintegration of polysterene concrete mix, to a certain drop in setting speed and to

air entrainment effect. The use of these chemicals utilizes a chemical reaction with

the chemicals present in the cement forming bonds resulting in improved concrete

properties like strength and workability.

On the other hand, Sathya, Bhuvaneshwari, Niranjan and Vishveswaran

(2014) centered their study on the effect of water hyacinth as bio-admixtures in

cement and concrete resulted that study reveals that the compressive strength and

setting time of cement are influenced by the bio admixture-hydro extract and bio

fine powder of water hyacinth. This is a novel approach evaluating the role of water

hyacinth on mechanical properties of concrete and cement. The setting time was

found to be delayed with increase in replacement percentage of bio admixture

whereas, the compressive strength and workability increased with increasing

concentration of bio admixture. The presence of photochemical such as lingo-

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Bantúg (Volume 9) 42

cellulose, saturated and unsaturated fatty acids have enabled to identify this bio

admixture as retarding but strengthening agent of cement and concrete.

Based on the study of Khan and Ullah (2004) investigated the effect of

retarding admixture (ASTM C 494 Type D) on setting time of cement pastes. The

setting time tests were performed under three different curing conditions

(temperature and relative humidity). The admixture was added to pastes made from

three different types of cements. The test results revealed that the effects of

admixture on setting time of cement pastes are dependent upon the type of cement

and dosage of the admixture. It caused set retardation of the three different types of

cements used, but with one type of cement it accelerated, the initial setting time and

retarded the final setting time when dosages higher than 0.25% were used.

Chalk

Chalk is a soft earthly variety of calcium carbonate, formed from the

remains of minute organisms. It also sometimes contains small amounts of silica,

alumina and magnesia. Its use as a material for cement manufacture is limited

(Hool, & Johnson, 1918). Chalks (dusty or dustless) are commonly made up of

limestone (CaCO3) and/or gypsum (dehydrated form of CaSO4) as their main

constituent. Kaolinite (hydrated aluminum silicate), carboxyl methyl cellulose

(CMC), poly vinyl alcohol, starch is present in small quantities. It may also

contain some impurities like silica and colored chalks contain some metals. Chalk

dust is major source of fine particulate matter in classrooms. Dustless or anti-

dusting chalks which are actually less dust producing chalks are available in

market. But these are less commonly used in developing countries because of their

high cost as compare to dusty chalks. Total amount of dust produced with dustless

chalks is less as compare to dusty chalks but contain high percentage of respirable

dust (<4.5µm), hence are not totally harmless (Nikam & Hirkani, 2013).

Few studies have explored the characteristics of chalk dust. Majumdar and

William (2009) observed that common chalk generates a higher amount of settled

dust (diameters < 4.5 µm and < 11 µm) than does anti-dust chalk. Likewise,

Majumdar et al. (2012) showed that Clean Write and Local Gypsum chalks

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generate the lowest and highest levels of Particulate Matters, PM1, PM2.5, PM5,

and PM10 when writing on a chalkboard, respectively. Chalk use has been

identified as a primary factor increasing the indoor aerosol concentration. They

analyzed the indoor PM2.5 content and observed high concentrations of calcium,

suggesting that indoor calcium originates from chalk dust. In addition, high

concentrations of coarse PM2.5-10 calcium have been attributed to chalk use in

the classroom. Based on the high calcium concentrations present in PM, they

concluded that chalk is a primary source of indoor PM10 and PM2.5.

Mortar

Mortar has been developed through an evolutionary process. It is a mixture

of cement paste and fine aggregate; in fresh concrete, the material occupying the

interstices among particles of course aggregate; in masonry construction, joint

mortar may contain masonry cement, or may contain hydraulic cement or most

commonly, Portland cement (American Concrete Institution, E3-13). The

Egyptians discovered that workable mortar could be produced by burning limestone

at high temperatures and soaking the by product (quicklime) in water after it cooled.

The quicklime was then mixed with volcanic ash or river sand to produce the first

lime mortars. Its primary function is to successfully bond unit masonry together.

Mortar’s presence is as crucial to a masonry wall system as the units it bonds

together (SEC 7-5, International Masonry Institute, 1997).

Mortar tests were designed to determine the effects of the various

admixtures on time of set, water reduction, shrinkage, and strength. Mortar used

in masonry works should conform on ASTM C-270 specifications. This

specification covers mortars for use in the construction of non-reinforced and

reinforced unit masonry structure Portland cements are commonly characterized

by their physical properties for quality control purposes. Their physical

properties can be used to classify and compare Portland cements. The challenge

in physical property characterization is to develop physical tests that can

satisfactorily characterize key parameters. This section, taken largely from the

PCA (1988), lists the more common U.S. Portland cement physical properties

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that are tested. Specification values, where given, are taken from ASTM C 150,

Standard Specification for Portland Cement. Also, Portland cements can be

characterized by their chemical composition although they rarely are for

pavement applications. However, it is a Portland cement’s chemical properties

that determine its physical properties and how it cures. Therefore, a basic

understanding of Portland cement chemistry can help one understand how and

why it behaves as it does. This section briefly describes the basic chemical

composition of a typical Portland cement and how it hydrates (American

Concrete Pavement Association, 2002).

Today, Portland cement is the most widely used building material in

the world with about 1.56 billion tones (1.72 billion tons) produced each year.

Annual global production of Portland cement concrete hovers around 3.8

million cubic meters (5 billion cubic yards) per year (Cement Association of

Canada, 2002). In the U.S., rigid pavements are the largest single use of

Portland cement and Portland cement concrete (American Concrete Pavement

Association, 2002). Further, the American Society for Testing and Materials

(ASTM) recognizes five types of Portland cement. These different cements are

manufactured from just about the same raw materials, but their properties are

changed by using various blends of those materials. Type I cement is the

normal cement used for construction, but four other types are useful for special

situations in which high early strength or low heat or sulfate resistance is

needed. Should the desired type of cement not be available, various admixtures

may be purchased with which the properties of Type I cement can be modified

to produce the desired effect. (McCormac, 2005)

Sieve Analysis

The value of an aggregate, sand or stone, with reference to its size may

be determined by means of a sieve analysis. This analysis consists of sifting the

material as supplied through different sieves, and then plotting upon a diagram

the percentage by weight which is passed (or retained) by each sieve—abscissae

(horizontal) representing size of grain and ordinates (vertical) representing

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percentage of any size passing each sieve. Such a sieve analysis may appear of

little use as regards the making and placing of 100,000 yd. of concrete, but

experiment has developed definite laws establishing the relation of percentages

and sizes of particles to maximum density and strength of concrete so that such

a sieve analysis may be directly translated into terms of commercial and

engineering economy (Hool, & Johnson, 1918).

Figure 1

Particle size distribution for fine and coarse aggregate

The grading of the aggregates used in concrete and mortar must fall

within the limits of coarse and fine aggregates grading (Figure1).

Table 1

Sieve Distribution of Aggregate Used in Mortar (ASTM C144) and Fine-

Aggregate Grading Limits (ASTM C 33/AASHTO M 6)

Sieve No. Opening Percent Passing (ASTM C144) Percent passing by

mass (ASTM C33) Natural Sand Manufactured Sand

4 4.75 mm 100 100 95 to 100

8 2.36 mm 95 to 100 95 to 100 80 to 100

16 1.18 mm 70 to 100 70 to 100 50 to 85

30 600 μm 40 to 75 40 to 75 25 to 60

50 300 μm 10 to 35 20 to 40 5 to 30 (AASHTO 10 to 30)

100 150 μm 2 to 15 10 to 25 0 to 10 (AASHTO 2 to 10)

200 75 μm 0 to 5 0 to 10

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1.1.4 Mix Ratios

The water-cement ratio (w/c ratio) theory states that for a given combination

of materials and as long as workable consistency is obtained, the strength of

concrete at a given age depends on the w/c ratio. The lower the w/c ratio, the higher

the concrete strength. Whereas strength depends on the w/c ratio, economy depends

on the percentage of aggregate present that would still give a workable mix. The

aim of the designer should always be to get concrete mixtures of optimum strength

at minimum cement content and acceptable workability (ACI, 1996).

Table 2

Relationship between Water-Cement Ratio and Compressive Strength

28-days compressive strength in psi

(MPa)

Water cement ratio by weight

Non-air entrained Air entrained

7000 (48.3) 0.33 —

6000 (41.4) 0.41 0.32

5000 (34.5) 0.48 0.40

4000 (27.6) 0.57 0.48

3000 (20.7) 0.68 0.59

2000 (13.8) 0.82 0.74

While the cement sand ratio is the ratio of the cement to the sand to be used.

There are four classes of mixture for mortars with varying cement sand ratio. The

table below shows the proportions for every class mixture. (Fajardo, 2000).

Table 3

Quantity of Cement and Sand for Mortar and Plaster in Cubic Meter

Class Mixture Proportion Cement in Bags Sand

40 kg 50 kg cu. m.

A 1:2 18.0 14.5 1.0

B 1:3 12.0 9.5 1.0

C 1:4 9.0 7.0 1.0

D 1:5 7.5 6.0 1.0

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Hydration of Cement

When a hydrous cement is mixed with water, a number of exothermic

chemical reactions take place both simultaneously and successively, commonly

denoted with the term hydration, in the very first period after the adsorption of water

on the surface of the dry powder, the dissolution of part of the inorganic phases

starts to occur. Very soon, however, new silicate and aluminate hydrated phases

begin to precipitate from the solution on the existing grains, thus favoring the further

dissolution of the anhydrous phases through an incongruent process (Ridi, 2010).

Mineral admixtures, such as fly ash and silica fume, can significantly reduce

the rate and amount of heat development, fly ash and silica fume modify different

stages of rate of heat evolution, for fly ash Various researchers have studied the

effect of fly ash on cement hydration determined that adding a low-calcium fly ash

reduces the heat of hydration of cement. (Al-Qadri, 2009).

Admixtures

Materials added to concrete during or before mixing are referred to as

admixtures. They are used to improve the performance of concrete in a certain

situation as well as to lower its cost. The addition of accelerating admixtures such

as calcium chloride to concrete will accelerate its early-strength development. The

results of such (particularly useful in cold climates) are reduced times required for

curing and protection of the concrete and the earlier removal of forms. Other

accelerating admixtures that may be used include various soluble salts as well as

some other organic compounds. Likewise, retarding admixtures are used to slow

the setting of the concrete and to retard temperature increase. They consist of

various acids or sugars or sugar derivatives. Retarding admixtures are particularly

useful for large pours where significant temperature increases may occur. They also

prolong the plasticity of concrete, enabling better blending or bonding together of

successive pours (McCormac, 2005).

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Consistency

Consistency is the relative mobility of a freshly mixed cement paste or

mortar or to its ability to flow. During cement testing, pastes are mixed to normal

consistency as defined by a penetration of 10 ± 1mm of the Vicat Plunger (ASTM

C187 or AASHTO 129). Mortars are mixed to obtain either a fixed water-cement

ratio or to yield a flow within a prescribed range. The flow is determined on a flow

table as described in Standard Specification for flow Table for Use in Test of

Hydraulic Cement (ASTM C230), and Standard Test for Flow of Hydraulic Cement

(ASTM C1437). Both the normal consistency method and the flow test are used to

regulate water contents of pastes and mortars, respectively, to be used in subsequent

test; both allow comparing dissimilar ingredients with the same penetrability or flow

(Kosmatka, & Wilson, 2011).

Setting Time

The elapsed time from the addition of mixing water to a cementitious

mixture until the mixture reaches a specified degree of rigidity as measured by a

specific procedure. Initial setting time is the elapsed time, after initial contact of

cement and water, required for the mortar sieved from the concrete to reach a

penetration resistance of 500 psi (3.5 MPa). While final setting time is the elapsed

time, after initial contact of cement and water, required for the mortar sieved from

the concrete to reach a penetration resistance of 4000 psi (27.6 MPa). (C 403/C

403M).

Compressive Strength Test

Compressive strength of cement mortar is undoubtedly a better criterion

by which to judge the sustainability of a cement for use in construction. The

American Society for Testing Materials has tentative specifications and methods

of tests for compressive strength of Portland-cement mortar which, when

adopted as standard by the Society, will be inserted in and made a part of the

American Specifications and Methods of Test for Portland Cement. A foreign

standard specification is as follows:

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Slowly setting Portland cement shall show a compressive strength of at

least 120 kg. per sq.cm. (1710 lb. per sq.in.) when tested with 3 parts by weight

of standard sand, after 7 days’ hardening, 1 day in moist air and 6 days under

water; after further hardening of 21 days in the air at room temperature (15° to

20°C.) the compressive strength shall be at least 250 kg. per sq.cm. (3570 lb. per

sq. in.). In case of controversies, only the test after 28 days is decisive. Portland

cement which is intended for use under water shall show a compressive strength

of at least 200 kg. per sq. cm. (2850 lb. per sq.in.) after 28 days’ hardening, 1

day in moist air and 27 days in water (Hool, & Johnson, 1918).

Figure 2

Effect of moist curing time on strength gain of concrete (Gonnerman and Shuman

(PCA), 1928)

Compressive strength test should conform to Standard Test Method for

Compressive Strength of Cement Mortars Using 2-in (50-mm) Cube Specimens

(ASTM C109/C109M-99).

Table 4 displays the strength of the concrete increases with age. After 7

days of curing, the strength of concrete will be 65–70 % in comparison to its

strength at 28 days of curing. Table 2 shows the strength of concrete at different

days in comparison to target compressive strength of concrete.

American Concrete Institute (ACI) Committee 301 recommends a

minimum curing period corresponding to concrete attaining 70 percent of the

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specified compressive strength. The often specified seven-day curing commonly

corresponds to approximately 70 percent of the specified compressive strengths.

The 70 percent strength level can be reached sooner when concrete cures at

higher temperatures or when certain cement/admixture combinations are used.

Table 4

Compressive Strength of Concrete Relative to Age (ASTM C150)

Age Strength in percent

1 16%

3 40%

7 65%

14 90%

28 99%

1.1 Research Objectives

The study aimed to determine the effect of chalk powder as additive in the

compressive strength of mortar. The study was conducted to gather data that

answers the questions: 1) What is the compressive strength of mortar having chalk

powder as admixture? 2) Does chalk dust increase the compressive strength of

mortar compared to mortar mixture without the presence of chalk powder? and 3)

Is it recommendable to add chalk powder in the production of mortar?

The primordial objective was to determine whether or not chalk powder

can be used as a major source of additive in the production of building or

masonry mortar, specially, this study aims to (a) to determine the physical

properties of chalk powder such as moisture content, specific gravity, and

density; (b) to determine the setting time of mortar with varying weight percent

addition of chalk powder for 24 hours; and (c) to determine the compressive

strengths of mortar with varying weight percent addition of chalk powder and

curing period and compare results to ACI provisions.

To achieve these objectives, the following hypotheses were tested at the

0.05 level of significance.

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H01: There is no significant difference on the average compressive strength

of masonry mortar with different percent replacement of chalk powder

with different curing period.

H11: There is significant difference on the average compressive strength of

masonry mortar with different percent replacement of chalk powder

with different curing period.

This study had the intention to determine the compressive strengths of

mortar specimens having chalk powder as percent admixture for cement

subjected at different days of curing period (7, 14 and 28 days).

The mortar specimens were made in a form of a cube (2 in x 2 in x 2 in).

These specimens were made following procedure outlined in ASTM C109 with

some modification. The mortar specimen without chalk dusts were made using the

1:2 Cement-Sand Ratio. Mortar specimens with chalk powder are made using 1:2

Cement-Sand Ratio and taking 5%, 10%, 15% and 20% of weight of cement as the

weight of chalk powder present in the mixture. The water cement ratio used is 0.485

based on ASTM C109.

METHODOLOGY

The Experimental Method of research was used in the conduct of this

study. All procedures were conducted and the resulting data were gathered and

used to determine if there is a significant difference between the independent

variable that is the different percentage of chalk dust and the dependent variable,

the compressive strength and setting time of the mortar specimens. Stated below

are the processes undertaken by this study.

Specimen Preparation

The outline of the conduct of the experiment was listed in order to perform

all the steps specified accordingly.

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2.1 Laboratory Analysis for Specimen Materials

The fine aggregate sieved were stored in an air-tight container in order to

prevent premature evaporation, hence losing the water content of the aggregate.

Physical properties of the fine aggregates and chalk powder such as its moisture

content, specific gravity, absorption and its density were determined using ASTM

procedures, respectively.

Determination of Moisture Content for Chalk Powder and Fine Aggregates

All moisture content analysis was based on the Standard Test Method for

Total Evaporable Moisture Content of Aggregate by Drying (ASTM C566). The

procedure was conducted on both materials, chalk powder and fine aggregates

(sand) in order to obtain the amount of water needed for the mixing of cement

and aggregates. The sand used during the mixing has a moisture content of

25.04% and conforming to the procedure stated by ASTM C566, the moisture

content of the chalk powder is 13.636%.

Determination of Relative Density, Density and Absorption Test for Chalk

and Fine Aggregates

The Standard Test Method for Density, Relative Density, and Absorption

of Fine Aggregate (ASTM C128) was used as a guide in determining the said

property of the aggregate. Determination of relative density of fine aggregates

was executed in order to determine the equivalent weights of materials by

volume while determination of the density of material were done to know the

weight of the material per unit volume. Absorption test were conducted to

determine the capacity of the aggregates to absorb water to adjust the water

requirement during mixing.

The relative density, density and absorption rate of sand used in the

experiment were as follows 2.154, 2308.994 kg/m3 and 12.416% respectively.

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The specific gravity and density of the chalk powder is 1.823 and 2000 kg/m3

respectively.

Sieve Analysis of Fine Aggregates

ASTM C136 was adapted to perform sieve analysis of fine aggregates

following grading limits provided by ASTM C33/AASHTO M6. ASTM C136

was adapted to perform sieve analysis of fine aggregates, following grading

limits provided by ASTM C33/AASHTO M6. Data were observed and

recorded.

Table 5

Sieve Analysis for Fine Aggregates Used and comparison to ASTM C33

US Sieve

No.

Opening

(mm)

Mass of

Sieve (g) Mass of Sieve

+ Sand (g) Mass

Retained (g) %Retained %Retained

(cum) %Passing

ASTM C33

Standard

Limit

Remarks

4 4.75 475.6 475.6 0 0 0 100 95 to 100 PASSED

8 2.38 486.0 503.8 17.5 3.50 3.5 96.5 80 to 100 PASSED

16 1.18 486.8 654.4 168.4 33.68 37.18 68.82 50 to 85 PASSED

30 0.600 478.5 628.7 150.0 30.00 67.18 32.82 25 to 50 PASSED

50 0.300 472.0 601.7 129.4 25.88 93.06 6.94 5 to 30 PASSED

100 0.150 468.0 498.2 30.0 6.00 99.06 0.94 0 to 10 PASSED

200 0.074 456.9 456.9 3.8 0.76 99.82 0.18

Pan 245.0 246.2 0.9 0.18 100 0

Total 500 100%

Table shows that the sand used passed the provisions stipulated in ASTM

C33 and does comply with the standard.

Preparation of Mortar

The researchers adapted procedures and guidelines in making mortar

specimen as stated in Standard Test Method for Compressive Strength of

Hydraulic Cement Mortars (ASTM C109).

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Proportion of Materials Calculation

For the mixture, 1:2 cement-aggregate ratio was used. A water cement ratio

of 0.485, as stated in ASTM C109, was used. For each category of percent addition

in the mortar mix, there were 15 mortar specimens, every five (5) of which were

subjected to a desired curing period. The percent addition of chalk powder to cement

categories are 0%, 5%, 10%, 15% and 20% by weight of the cement.

Mortar Mix

The procedure used for mixing and making the mortar specimens were

based on ASTM C109. The mortar mix was tamped in each cube as stated in ASTM

C109. This procedure was performed in all mortar specimens made of different

percentage chalk dust content.

Determination of Setting Time of Mortar Mix

The bearing surface of the Gillmore apparatus needle for initial setting

time were brought in contact with the mortar. The needle was released and

allowed to penetrate the surface.

The initial setting time of mortar was recorded as the time when the needle

cannot penetrate anymore the surface of the mortar. After 15 minutes interval, the

penetration test for the initial setting time was repeated on areas other than the area

where the previous penetration was done. Then, steps were repeated using the

needle for the final setting time. The final setting time of the mortar were recorded

as the time when the needle cannot penetrate anymore any of the bearing surface of

the mortar. Finally, the time for the final setting time was recorded.

2.2 Storage and Curing of Mortar Specimens

The storage and curing of mortar specimens were also based on ASTM

C109. The specimens were immersed in water in a storage tank and left for curing

period of 7 days, 14 days, and 28 days.

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

55 Bantúg (Volume 9)

Compressive Strength Test

Compression Strength Testing Machine was used to determine the

compressive strength of the mortar specimens having different percent

composition of chalk dust. Compressive strength test result should conform to

provisions stipulated in ACI Mix Design.

Mortar specimens were wiped off in such a way that it was in a surface dry

condition. Any unnecessary dirt’s occurring on the plane surface of the machine

were removed. The five specimens of different curing period and percent

composition of chalk powder were subjected to the testing machine in order to

determine their compressive strengths. The specimens were loaded until point of

rupture. Then, their compressive strengths indicated in the gauge of the machine

during time of rupture were recorded.

Data Analysis

The statistical test used to determine if there is a significant difference

between the compressive strengths of the mortar specimens using different types of

water is the One-Way-ANOVA. It was used to determine if there is a difference in

the resulting compressive strength of mortar specimen with chalk dust to the ones

having no admixture. The stepwise method of solving is implemented to calculate

for the f-value using 5% level of significance. The computed f-value that is greater

than the tabular f-value was used as an indicator whether the groups are significantly

different from each other or not. If the f – value computed is greater than the

tabular f – value, the remark is significant. Otherwise, the remark is insignificant.

Tukey-HSD Test was also used to determine where the difference between

groups lies. The Tukey-HSD test or Tukey’s Honest Significant Difference test

is a post-hoc test based on the studentized range distribution. The One-way

ANOVA employed imparts idea if the results imply a significant difference

between the groups but this test won’t tell you where exactly the difference lies,

thus Tukey-HSD Test is employed to determine which groups differ. (Stephanie,

2016)

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

Bantúg (Volume 9) 56

RESULTS

Setting Time of Mortar Mix with varying percentage of Chalk Powder

Using the Gillmore Apparatus, initial and final setting time of the mortar

mix were recorded in an interval of 15 minutes.

Figure 6

Bar Graph for setting time of Mortar Mix

Figure 6 shows that mortar mix with no chalk powder added has the

quickest setting time. From the graph, it could be clearly seen that upon addition

of chalk powder, the final time of setting increases. As more chalk powder is

added onto the mortar, the slower the mortar mixture will set.

Mean Compressive Strength of Mortar Specimens

This section presents the compressive strengths of mortar cubes made using

five different percentage of chalk added to mortar mix and cured for 7, 14 and 28

days.

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

57 Bantúg (Volume 9)

Table 6

Results of Mortar Test for Compressive Strength

Percent

Addition of

Chalk Powder

Mean Compressive Strength (psi)

7 days 14 days 28 days

0% 4600 6820 7280

5% 4280 6360 6600

10% 2260 5160 6260

15% 2220 3040 4760

20% 2100 2440 3280

As shown, as the amount of percentage of chalk added increases, the

compressive strength of the mortar decreases.

3.1 Comparison of Compressive Strengths to ACI Provision

Since a water-cement ratio of 0.485 was used in the mixing process, by ACI

Mix design, mortar specimen has to achieve a strength of 5000 psi.

Table 7

Comparison of Result to ACI Mix Design (28 days)

Different

Percentage of

Chalk Added

Compressive

Strength (psi)

ACI Mix Design

Standard Limit Remark

0% 7280 5000 psi

(Based on 0.48

water-cement

ratio)

Passed

5% 6600 Passed

10% 6260 Passed

15% 4760 Failed

20% 3280 Failed

As shown, it was observed that only 0%, 5% and 10% of chalk powder

added passed the design strength of 5000 psi.

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

Bantúg (Volume 9) 58

3.2 Statistical Tests Employed

One-Way ANOVA. Table 9 shows the result of the conduct of analysis of

variance on the resulting compressive strength of mortar specimen having different

percentage of chalk powder added at different days of curing. The tabular f-value

based on degrees of freedom of groups is 2.87. The f-value computed in all analyses

was higher than the tabular f-value, hence, there is a significant difference between

compressive strength of mortar with different percentage of chalk powder added.

Table 8

Analysis of Variance for Compressive Strength

Days of

Curing

Sources of

Variation

Degrees of

Freedom

Sum of

Squares

Mean

Squares

f-Value

Computed Tabular

7

Between

Groups 4 30 610 400 7 652 600

394.46 > 2.87 Within

Groups 20 388 000 19 400

Total 24 30 998 400 SIGNIFICANT

14

Between

Groups 4 76 521 600 19 130 400

255.75 > 2.87 Within

Groups 20 1 496 000 74 800

Total 24 78 017 600 SIGNIFICANT

28

Between

Groups 4 51 697 600 12 924 400

145.22 > 2.87 Within

Groups 20 1 780 000 89 000

Total 24 53 477 600 SIGNIFICANT

From the table, the comparison between different percentages of chalk

powder resulted to have a significant difference among them thus the post hoc

test, Tukey-HSD Test, was conducted.

Tukey-HSD Test. If the mean difference of groups is higher than the

value of HSD, there is a significant difference between compressive strength of

mortar with different percentage of chalk powder added, otherwise, insignificant.

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

59 Bantúg (Volume 9)

Table 9

Tukey-HSD Test Result for Compressive Strength of Mortar (28 days)

Comparison Mean Difference HSD Remark

0% vs 5% 680 > 528.329 Significant

0% vs 10% 1020 > 528.329 Significant

0% vs 15% 2520 > 528.329 Significant

0% vs 20% 4000 > 528.329 Significant

5% vs 10% 340 < 528.329 Insignificant

5% vs 15% 1840 > 528.329 Significant

5% vs 20% 3320 > 528.329 Significant

10% vs 15% 1500 > 528.329 Significant

10% vs 20% 2980 > 528.329 Significant

15% vs 20% 1480 > 528.329 Significant

As shown, comparison of 5% vs 10% deemed to have no significant

difference. Others resulted to have a significant difference.

As summary, chalk powder as admixture affects the resulting compressive

strength of mortar. The results showed that the compressive strength decreases as

more chalk powder was added on the mix. At 5% -10% addition of chalk powder

to mortar mix, the strength decreases for some amount but still passed the standard

limit prescribed by ACI. 20% addition of chalk powder greatly decreased the

strength of the mortar specimen and failed to pass the standard limit. As a result,

5% - 10% by weight of cement as weight of chalk powder to be added can be used

as admixture for mortar use since both passed the design mix of 5000 psi.

CONCLUSION

Data were gathered in order to evaluate if there is a significant difference

in the compressive strength of masonry mortar having different percentage

addition of chalk powder in varying days of curing.

With the following results gathered and analyzed, it appeared that the

compressive strength of the mortar mixture having 5% and 10% of chalk

powder had differed for about 10% and 14%, respectively, of the strength of

mortar mixture without any admixture. Clearly it seems that the design strength

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture

Bantúg (Volume 9) 60

used (5000 psi), amidst they differ for about 10% - 15% of the strength of

mortar without admixture, it passed the prescribed design strength.

Using the data resulted from the analysis, it can be concluded that 15% -

20% of chalk powder added to mortar mix should not be used as masonry mortar as

it greatly reduces the strength of mortar specimen. Only 5-10% chalk powder added

is reasonable to use as it produces a strength close enough to the design mix used.

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