Comprehensive strength of masonry mortar with chalk powder ...

Comprehensive Strength of Masonry Mortar with Chalk Powder as Admixture
Bantúg (Volume 9) 38
powder as admixture
Mujahid A. Dagadas
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
39 Bantúg (Volume 9)
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.
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,
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-
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
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
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
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
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
28-days compressive strength in psi
(MPa)
Non-air entrained Air entrained
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
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).
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 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:
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
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
Age Strength in percent
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.
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.
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.
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
+ Sand (g) Mass
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).
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.
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)
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.
Percent
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
Different
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.
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
Days of
394.46 > 2.87 Within
14
Between
255.75 > 2.87 Within
Total 24 78 017 600 SIGNIFICANT
28
Between
145.22 > 2.87 Within
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.
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
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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