Concrete is a construction material composed of cement commonly Portland cement as well as other cementitious materials such as fly ash and slag cement; aggregate, water, and chemical admixtures. Its uses date back to early 3000 BC by Egyptians. It is said that the Romans used a primal mix for their concrete consisting of small gravel and coarse sand mixed with hot lime and water, and sometimes they even used animal blood as the binder. The Assyrians and Babylonians used clay as the bonding substance or cement whereas Egyptians used lime and gypsum cement.
With the growing industrialization and urbanization, there is corresponding growth in demand for modern infrastructure, for which, Portland cement concrete has emerged as the material of choice. Its consumption has risen to the millions of tons per year .The production of each ton of Portland cement releases approximately one ton of carbon dioxide which is one of the gases responsible for global warming.
The concrete industry is taking necessary steps in reducing local and global environmental aspects and cost reduction techniques. The readily available industrial waste products like Fly ash, granulated blast furnace slag, silica fume, rice husk-ash, sugarcane ash and natural pozzolans stands to be the perfect partial replacement for cement in the concrete mix, reducing environment impacts and costs. The utilization of pozzolanic materials like silica fume, Rice Husk ash, fly ash and metakaolin for partial replacement in concrete had been used and studied widely.
The replacement of cement by pozzolanic materials have many advantages such as improving the cementitious properties, reducing the total energy, production cost and carbon dioxide emission.
The advances of concrete technology show that the use of mineral admixtures is necessary and essential for producing high performance concrete. In recent years, there has been a growing interest in the use of metakaolin (MK) for this purpose.
1.2 Metakaolin
MK is a thermally activated alumino silicate material obtained by calcining kaolin clay within the temperature range of 700-850°C. It contains typically (50-55%) SiO2 and (40-45%) Al2O3 and is highly reactive. It has been reported that the replacement of cement by (5-15%) MK results in significant increases in compressive strength for high-performance concretes and mortars at ages of up to 28 days, particularly at early ages. The replacement also results in improved concrete durability properties, including the resistance to chloride penetration, freezing and thaw in the cement paste and deicing salting scaling (Poon, et al. 2001).
In accessing the pozzolanic activity by the standard test methods for sampling or testing fly ash or natural pozzolans for using replacement in the Portland cement concrete paste, it requires a long time (normally 7 or 28 days) to obtain pozzolanic properties in terms of strength activity index.(ASTM C 311, 1998).
Therefore, there is a need of test method to determine the pozzolanic activity of the natural pozzolans to be used as cement replacement in very short duration of time. That will help in selecting appropriate pozzolans to be used as cement replacement at faster rate. The incorporation of pozzolanic materials in cement mortar and mass concrete production as replacement of cement increases economical and technological benefits.
1.3 Statement of the Problem
Metakaolin, one of the natural pozzolan is used as the cement replacement at various quantities. The chemical behavior of the MK depends upon calcining temperature of kaolinite and the combustion time.
MK when used as mineral admixture in Portland cement Concrete, the test method for determining its pozzolanic activity is according to ASTM C311; which says the compressive strength of mortar at 28 days is required to determine its strength activity index but in usual construction works using mineral admixture in Portland cement concrete, the assessment of quality of the concrete is must at earliest time in order to ensure the quality of built structure using MK as cement replacement.
Therefore knowing the quality of MK used cement concrete at earliest time helps to monitor the pozzolanic activity and the properties can be adjusted to fulfill the desired quality in Construction.
From the scientific point of view and for numerous industrial applications, simple but accurate methods to determine pozzolanic activity of metakaolin mortar are important. The development of such techniques is also of practical and economical importance and constitutes a topic of scientific interest. In this research the electrical conductivity is recorded experimentally. It can be easily determined and correlated with the Ca (OH) 2 concentration.
In order to address above problem it is very essential to develop comprehensive method to evaluate pozzolanic activity of MK which in this study is will be done using conductivity measurement techniques using Ca(OH)2 solution.
1.4 Objectives
The main objective of the study is to experimentally determine the conductivity measurement techniques for evaluation of pozzolanic activity of Metakaolin.
Various studies had been carried out on Pozzolans as cementitious replacement in OPC using standard Ordinary Portland Cement solution, but in this study Ca (OH) 2 will be used to determine electrical conductivity measurements which will directly determine the pozzolanic activity of MK.
The material under this study is local materials using readily available testing equipments to determine the conductivity measurement of Metakaolin/lime reaction. The various objectives under this study can be listed as
The pozzolanic activity of Metakaolin: To set up rapid method in determining evaluation of pozzolanic reactivity of MK using Ca(OH)2 solution at various conditions like suspension temperature, percentage variation of used sample.
Compressive strength of Metakaolin cement paste at various percentage cement replacement and correlate strength activity index and compressive strength of metakaolin/cement mortar.
To determine various properties of MK like fineness, strength activity index, chemical composition etc.
1.5 Scopes of the Study
Effects of Reaction temperatures of test solution at 40 °C, 50C°, 60C, 70° C and 80°C. The temperature at range (0-40°C) is not desirable because of slowness of pozzolanic reaction and temperature above 80°C gives technical difficulties due to higher vapor pressure and water loses from the thermo stated vessel as it is evident from many of the studies done.
To determine the compressive strength of MK cement mortar at 7, 21, 28, 56 and 91 days of various percentages cement replacement by Metakaolin.
CHAPTER 2
LITERATURE REVIEW
2.1 Pozzolans
Pozzolan is a siliceous or siliceous and aluminous materials, which possesses little or no cementitious properties, in finely divided form and in presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds, possessing cementitious properties.
According to the ASTM C618, Pozzolans are classified into three different classes. The major chemical components of pozzolans are SiO2, Al2O3, Fe2O3, which are some of the indicators to classify pozzolan.
Class N. It is a raw calcined natural pozzolans which are volcanic ashes ,pumicites opaline shales and cherts, calcined diatomaceous earth and burnt clay ,rice husk ash or agricultural ash
Class F and
Class C. Class F and C pozzolans like fly ash, silica fume and granulated blast-furnace slag.
Figure 2.1 Different Types of Pozzolans.
2.2 Natural Pozzolans
Natural pozzolans are those present on the Earth's surface such as diatomaceous earths, opaline cherts, volcanic ash, shales, tuffs and pumicites.
Natural pozzolans have been used in dams and bridges to lower the heat of hydration and increase resistance of concrete to sulfate attack and control the alkali-silica reaction.
In the United States, volcanic tuffs and pumicites, diatomaceous earth, and opaline shales are found principally west of the Mississippi River in Oklahoma, Nevada, Arizona, and California.
Metakaolinite is obtained by heating kaolinite at 700-850 °C. It is a poorly crystalline transition phase which behaves as highly reactive artificial pozzolan. Nowadays, the properties of calcined clays are widely discussed in cement literature for their pozzolanic properties (Saad, et al., 1982). Metakaolinite reacts with calcium hydroxide and water to yield hydrated compounds of Ca and Al silicates. The pozzolanic activity of metakaolinite depends on the cristallinity of the kaolinite .Various studies shows that some activated materials such as metakaolin (MK), which is produced by heating kaolinite, have been shown to be an excellent pozzolan. The abundance of kaolinite is known in commercial deposits and in the C horizon of soil profiles in tropical regions which makes it not only economically attractive, but environmentally desirable for use as an addition or part replacement of ordinary Portland cement in the manufacture (Bich, 2001).
Metakaolin is a highly reactive pozzolan having high specific surface area that makes it as suitable pozzolanic material to be used in concrete. The smaller particles of MK much denser and impervious concrete which are have high resistance to sulphate attacks. It changes the porous structure in cement paste, mortar and concrete and improves the resistance to the transportation of water and diffusion harmful ions which lead to degradation of the matrix. Studies show that metakaolin particles are nearly 10 times smaller than the cement particles thereby making concrete denser and impervious.
2.3 Artificial Pozzolan
The artificial pozzolans are produced during various thermal treatments such as burnt clay and shale, fly ash, slags, ground ceramic materials, etc.
Figure 2.2 Groups of Pozzolans
2.4 Pozzolanic reactivity of Metakaolin.
The lime reactivity of MK depends on the factors like particle size, surface area and its mineral composition. There are numerous methods to determine its pozzolanic activity classified as direct and indirect methods.
The development of the lime MK reaction causes the formation of insoluble products, therefore diminishing the calcium hydroxide concentration in the solution. As a result, a decrease of conductivity takes place whose change rate depends on whether the reactivity of the pozzolan is higher or lower. The decrease of free Ca ions due to the increase of the CSH-products produces the decrease of conductivity takes place whose change rate depends on whether the reactivity of the pozzolan is higher or lower. Calcium Hydroxide is liberated during the Hydration of Port Land Cement, the pozzzolans combine with this liberated calcium hydroxide to form stable cementitious compounds which contribute to strength and water tightness (Jun Xie, 1996).
Al2O3.2SiO2 + 3Ca (OH) 2 + nH2O
C-S-H + C2ASH8
Calcium Silicate Hydrates + Calcium Alumino Silicate Hydrate
Metakaolin Calcium hydroxide
B.B.Shabir, reported that the chemical reactions involved when calcined clays are used as pozzolans is that between the AS2 and the CH derived from cement hydration, in presence of water. This reaction forms additional cementitious aluminium containing CSH gel, together with crystalline products which include calcium aluminate hydrates and alumino-silicate hydrates (C2ASH8, C4AH13 and C3AH6).
Wild, et al, 1996 examined the effect of metakaolin content on relative strength at 1day and at 90 days. At day one, contribution due to pozzolanic activity is expected to be small, the relative strength increases with increase in MK content up to a maximum of 1.18% at 10% replacement and then falls linearly to 0.76%. The increase in relative strength at day 1 is interpreted as due to increased acceleration of OPC hydration combined with contribution from the filler effect and fall in relative strength at high metakaolin contents must be due to dilution effect. At 90 days all the cementitious reactions are near completion and short term effect of relative strength enhancement due to acceleration of OPC hydration has been lost.
W. J. McCarter and D. Tran (1996) studied the pozzolanic activity by direct activation using calcium hydroxide by conductivity method and reported the conductivity response into four distinct regions. Region I extending over the initial 4 h, during which the conductivity was seen dropping by about 10% of its initial value. He attributed the drop due to initial chemical reaction between the particles and can be taken as indicator of pozzolanic activity. It is followed by a period extending up to approximately 14 h where the rate of change of conductivity remains relatively constant and attains a low value. This is denoted as Region II. Such a low rate of change of conductivity would indicate a reduction in chemical activity within the paste in comparison to Region I. This could be classified as a dormant period. He reported that, at approximately 14 h, and up to 22 h, (denoted as Region III), there is drop in conductivity which is taken to indicate an increase in rigidity of the paste, i.e. setting.
Region IV occurred at periods in excess of 22 h as, at this point in time, there is another distinct change in the rate of change of conductivity. The reduction is attributed to a slowing down in chemical activity.
Figure 2.3 Conductivity responses using a saturated CH solution
(W. J. McCarter and D. Tran)
Fraas and Cabrera, 2000 studied influence of Metakaolin on the reaction kinetics in MK/lime and MK-blended cement systems at 20°C. They prepared five mortar pastes containing 0%, 10%, 15%, 20%, and 25% of metakaolin keeping water binder as 0.55 by weight. The hydration times were from 1 to 360 days. These metakaolin mixtures were placed in plastic airtight containers and then left for curing at 100% relative humidity. DTA and XRD were used to get information on reaction kinetics of the pozzolanic-lime as well as MK-cement reactions. The results obtained here from DTA analysis showed the sequence of phase development, C2ASH8 and C4AH13, to be closely related to matrix used. In the metakaolin lime matrix (1:1in weight), C2ASH8 is formed in parallel with the C4AH13, increasing their contents with the hydration time. However, in blended cement matrices (up to 25% of MK), C2ASH8 is the main hydrated aluminate compound and only a small amount of C4AH13 is detected in matrices cured longer than 180 days and with MK contents at least 20%.
2.5 Methods of Determining Pozzolanic Activity
The evaluation of MK pozzolanic activity can be carried out by various mechanical and chemical methods using several techniques. The testing period for different techniques is the question of concern. While evaluating the pozzolanicity of MK cement paste by means of compressive strength development, usually longer period of testing time is required therefore an alternate and efficient method becomes a trying step. Various researches had tried different methods to evaluate pozzolanic activity of fly ash.
S.K. Agrawal, 2004 reported in his study about determining the accelerated pozzolanic activity of various siliceous materials like silica fume, fly ash etc with varying fineness by compressive strength development of the concrete mix using pozzolans. The cement pozzolan mortar cubes was cured for 7 and 28 days. In comparison of accelerated pozzolanic index with 28 days strength of mortar cubes stored for 28 days, there was good correlation in the results in development of compressive strengths for 7 days and 28 days.
C. Bich et al. studied the pozzolanic activity of metakaolin at different time periods at 7, 28, and 90 days on pastes composed of 50% calcium hydroxide and 50% metakaolin, hydrated at normal consistency, according to the French standard NFP 15-402 (Ambroise, 1984).
Mini-cylinders of metakaolin paste were casted in Plexiglas moulds having diameter as 20 mm, height of sample as 40mm keeping at temperature of 20 °C until the day before the desired time period. Then, they were dried at 50 °C for one night and ground to get desired particle size less than100 μm. The powders were subjected to DTA analysis, and the pozzolanic activity was defined as the calcium hydroxide consumption versus time measured by the residual DTA peak of calcium hydroxide.
T. Yamamoto, et al, 2006 examined an API (assessed pozzolanic-activity index) method to evaluate pozzolanic reactivity of fly ash using K- value as per Feret's law; which states that the strength is proportional to [c/(c + w + a)]2 , where c, w and a are the volumes of cement, water and air, respectively. Two types of mortars were used with different water ratios.
They calculated K-values from the following formula: S = K [(c + f)/(c + f + w + a)] 2. Where S is the compressive strength of mortar and f is volume of fly ash. Fly ash was counted as a cement material. To check the adequacy of the API method for the pozzolanic evaluation, the activity index was compared.
The authors concluded following facts.
i) The K-value is useful to estimate the degree of the pozzolanic activity of fly ash in mortar.
ii) The API method is one of the most useful and rapid methods to evaluate the degree of pozzolanic activity of fly ash, because API has a good relation to the K-value.
Greenberg describes a method based on the use of a conductometric technique to indirectly monitor the depletion of lime by measuring the electrical conductivity of the test solution as the reaction proceeds. Other indirect methods are based on the strength development occurring with reaction time.
Luxán,et al, 1989 proposed a very simple, rapid and effective, also based on electrical conductivity measurement of aqueous suspensions for evaluating the pozzolanic activity of natural pozzolans. They, from the measurements of the conductivity variations of natural pozzolanic materials in different aqueous media and taking into account the theoretical definition of pozzolanicity, established the following facts related with their proposed method.
The reaction between calcium hydroxide in aqueous solution and pozzolanic material as finely divided powder produces a decrease in electrical conductivity of the solution due to fixation of dissolved Ca (OH)2 by pozzolan particle surface.
They reported that only 120 s were necessary for evaluating pozzolanicity of tested natural products, and the pozzolanic material was classified in with respect to variation in conductivity of the pozzolans.
In the evaluation of metakaolin pozzolanic activity by conductrometric techniques , calcium hydroxide (which is the product of hydration between cement and water in the concerte paste) is proposed to produce metakaolin mortar pastes at various reaction temepratures. It possesses the property of electrical conductivity which is dependent of concentration of Ca2+ and OH- ions in the solution. Several studies had been carried out to moniter the pozzolanacity of natural pozzolans directly using OPC and pozzolan mortar pastes.S.Sinthaworn et al proposed a alterntaive technique for quick monitering of pozzolanic reactivity of pulverised fly ash within 28 hours of testing time.The evaluation of pozzolanic reactivity was based on change in electrical conductivity for tested pozzolans in OPC solution.The solution was obtained by mixing water and OPC at suspension temperature at 80° C . The electrical conductivity was recorded by electrical conductivity meter.
As it is known from various studies carried out in the past, lime (or cement)-metakaolin reactions kinetics and evaluation of its pozzolanic activity are not yet very well understood and have been the subject of investigation of many researchers. The study of the pozzolanic activity of metakaolin is of great scientific interest and of technological importance as well to suit the need of reactive admixture in concrete industry.
CHAPTER 3
METHODOLOGY
This chapter mainly describes experimental methods, preparation of materials which will be used in this study.
3.1 Experimental Program
This part of study involves in the investigation of pozzolanic activity of the tested pozzolan through conductivity measurement and compressive strength of mortar mixed with pozzolan according to ASTM C 311. Blaine air permeability measurement techniques will be used to determine the degree of fineness of the tested pozzolan. X-ray Diffraction (XRD) test will also be carried out to determine the basic properties of Metakaolin.
The methodological framework of this research will be carried out as per processes outlined below.
Preparation of the materials required for the study and its preliminary investigation.
Experimental schemes dealing with its basic properties.
The main experimental program- conductometric technique.
Compressive strength test to determine strength activity index of the metakaolin with ordinary Portland cement.
Investigation of the results in order to propose technique to evaluate pozzolanic activity of Metakaolin.
Start
Preparation of Samples
Chemical Composition
Experiments on Basic Properties
Fineness
Chemical Composition
Compressive Strength
Strength Activity Index IndecIndex
Duration
Chemical Composition
Suspension Temperature
Conductometric Test
Dosage
Chemical Composition
Feed to PC Analysis
Data Analysis
Monitoring Conductivity
End
Figure 3.1 Flow Chart Showing Total Experimental Framework.
3.2 Materials.
3.2.1 Ordinary Portland cement
Ordinary Portland Cement (OPC) Type I, Elephant brand produced by Siam Cement Co. Ltd. conforming to ASTM C-150 was used throughout the study. All 50 kg bag of cement were each encased in additional plastic bags, upon delivery, and stored in dry place.
3.2.2 Metakaolin
The kaolin will be obtained from Ranong and Lampang Province of Thailand. The kaolin will be burnt at 800°C in the incinerator for 6 hours. After being thermally activated, kaolin will be converted into pozzolan called Metakaolin (MK).Then; the metakaolin will be ground in the grinding machine for one hour. The specific surface area can be obtained by using Blane air-permeability apparatus conforming to ASTM C 204. The composition of the MK will be reported as per table below.
Table 3.1 Details of physical and chemical properties of Metakaolin
Oxide
Metakaolin (%)
Silica(SiO2)
Alumina (Al2O3 )
Iron Oxide (Fe2O3)
Calcium Oxide(CaO )
Magnesium Oxide(MgO)
Sodium Oxide(Na2O)
Potassium Oxide (K2O)
TiO2
LOI
Physical property
Surface area (m2/g)
Density (g/cm3)
(b)
Figure 3.2 (a) Incinerator, and (b) Grinding Machine
3.2.3 Calcium Hydroxide
An analytical grade calcium hydroxide, Ca (OH) 2 powder, Univar brand, complying with analytical reagent by Ajax Finechem Pvt.Ltd, will be used. The above stated reagent is a highly pure fine chemical powder that is used for industrial application and research. It will be kept in a sealed container throughout the experiment. A solution of calcium hydroxide, called lime water will be prepared by adding distilled to calcium hydroxide powder. The mixture will be shaken thoroughly for every hour for a period of not less than 24 hours to make sure that as much calcium hydroxide dissolves as possible in distilled water. The calcium hydroxide will be left to settle and the solution will be siphoned off from the sediment.
3.2.4 Fine Aggregates
The fine aggregate to be used in casting cement mortar specimens was air dried and sieved by mechanical sieving machine to obtain required grading according to ASTM C 33 (1999). The sieved river sands will be stored separately in clean, dry plastic bags to avoid contamination from other impurities. The physical and mechanical properties like absorption, bulk specific gravity, apparent specific gravity and fineness modulus will be investigated.
The sand will be graded between upper limit and lower limit by following the standard. Specific gravity and absorption of fine aggregate will be tested according to ASTM C-128. Grading and the physical properties of fine aggregate will be shown as in the table below.
Table 3.2 (ASTM) Grading and Testing of Physical Properties of Fine Aggregate.
Type of Test.
Related ASTM Standard.
Fineness Modulus
ASTM C 33-99
Bulk Specific Gravity
ASTM C 128-93
Bulk Specific Gravity (SSD)
ASTM C 128-93
Apparent Specific Gravity
ASTM C 128-93
Absorption (%)
ASTM C 128-93
3.2.5 Mixing water
Ordinary tap water will be used in casting mortar cubes for testing compressive strength whereas distilled water will be used in lime solutions. The electrical conductivity of tap water and distilled water will be measured and reported as micro-Siemen/centimeter.
3.3 Experimental Determination of Basic Properties of MK
This part of study involves investigation of the pozzolanic reaction through basic properties and compressive strength of mortar specimen mixed according to ASTM C 311.The chemical composition and degree of fineness of the pozzolan is determined by Blaine air permeability test .The testing method and theories behind each method is explained below.
3.3.1 Light Scattering Technique.
The physical composition like particle size and specific surface area of the pozzolan will be determined by using light scattering techniques at the National Metal and Minerals Technology Center (MTEC). This method will be used to verify and compare the fineness that would be determined by Blaine air permeability measurement according to ASTM Designation C 204-00.
3.3.2 Blaine Air Permeability Test
Blaine air permeability apparatus is used to determine fineness of Portland cement in terms of specific surface expressed as total surface area in square centimeters per gram of cement. The apparatus consists of: calibrated U-tube manometer, ground glass joint, stainless steel test cell and plunger, rubber aspirator bulb and perforated disc and also includes 8 oz. (226.8g) bottle of red manometer fluid, filter paper, filling wood block for holding test cell during and funnel mounted on finished wood panel with rubber-footed base. The apparatus meets specification prescribed by ASTM C204; AASHTO T153.
The theory of the Blaine air permeability measurement is based on the resistance of air when it flows through a given thickness of powder. The resistance to air is higher if the space between the particles is narrower which is dependent on the particle size of powder. The smaller the particle sizes of the powder, the narrower the space between the particles. So it takes longer time for air to pass through the powder which is finer than the layer of coarse of powder.
The specific surface area of the particle can be calculated using the following equation according to ASTM Designation C204-00.
S= Specific surface area of the test material (m2/kg).
Ss=Specific surface area of the standard cement used in calibration of the apparatus (m2/kg).
t= measured time interval of manometer drop for test materials.
ts= measured time interval of manometer drop for test materials.
= porosity of a prepared bed of test material.
= porosity of a prepared bed of standard cement.
= density of test material (kg/m3)
= density of standard cement (3150 kg/m3)
b = apparatus constant. For Portland cement, value of b is 0.9 as recommended in the ASTM C 204-00.
3.3.3 X-ray Diffraction (XRD)
X-ray diffraction tests were conducted to investigate the mineralogical composition of Metakaolin. The test was conducted in Department of Chemistry, Faculty of Science, and King Mongkut's Institute of Technology. X-ray Diffraction in powder diffraction method was applied with Voltage 40 kV and current 40 mA. It was analyzed over the scanning range from 10° to 70° 2-theta-scale.
Figure 3.3 X-ray Diffraction Apparatus
3.4 Strength Activity Index
All tests will be carried out as per ASTM Designation C 311-98 which specifies sampling and testing of pozzolans to be used as admixture in Portland cement Concrete. The strength activity index is the ratio between the compressive strength of a test mixture and a control mixture that is calculated as per equation below. ASTM Designation C 311-98 is used to determine the pozzolanic reaction of pozzolan.
Strength activity index with Portland cement= (X/Y) x100.
X-Average compressive strength of test cubes, and
Y-is the average compressive strength of control cubes.
As per ASTM Designation C 311-98 b, the mixture to be used as control consists of 500 grams of Portland cement and 1375 grams of graded standard fine aggregate (sand) and 242mL of water. The test mixture consists of 400 grams of Portland cement, 100 grams of pozzolan, 1375 grams of graded standard sand. Replacement levels of OPC by MK chosen for the concrete mixes will be 0, 5,10,15,20 and 25%.The water requirement is being controlled by flow of ±5 mm of control mixture. Three cubes of sampling per specimen are required to test compressive strength at 7, 28, 56 and 91 days.
Three (50x 50 x 50 mm) mortars cubes will be molded both from control mixture and from a test mixture as per ASTM Designation C109. The mortar cubes will be controlled at water to binder ratio of 0.45. After molding, the specimens will be cured until the day of testing.50 mm cubes will be tested for compressive strength using Universal Testing Machine. Compressive strength will be calculated by dividing the maximum load attained during the test by cross sectional area of the tested specimens.
All the specimens will be tested at the age of 7, 14, 28, 56 and 91 days. The average compressive strength will be calculated among the three cubes of specimens from the same mixture at the same testing age and the strength activity index with Portland cement will be calculated.
3.5 Enhance Conductivity Measurement Technique
The evaluation of pozzolanic activity of the pozzolan (Metakaolin) in this study will be determined by means of chemical reaction of the pozzolan. The change in electrical conductivity of the test solution will be the basis of determination of pozzolanic activity of Metakaolin. The rate of change and variations of electrical conductivity will be used for evaluation. The evaluation of pozzolanic activity will be studied and investigated based on change in electrical conductivity of the solution obtained from pozzolan and calcium hydroxide at different suspension temperature. The conductivity will be continuously recorded by using electrical conductivity meter and data will be stored by using personal computer.
The electrical conductivity measuring set consists of a conductivity meter (model Cond 340i WTW brand from Germany) with thermometer, a hot plate for temperature control, carbonation protection and computer interface. A beaker will be used for testing solutions. The glass stopper of capacity 250 mL Pyrex brand from Germany will be used in the experiment. Rubber corks will be used as carbonation protectors when installed on the stopper.
Conductivity sensors are made of durable corrosion- resistant materials. It doesn't need any maintenance other than cleaning to remove contaminants. The sensor probe will be cleaned by soaking in water or weak acid after taking every measurement. The electrical conductivity meter to be used in the experiment will be regularly calibrated from a standard solution.
The saturated calcium hydroxide solution will be prepared by gradually adding calcium hydroxide powder to distilled water, and shaking every few hours for period of 24 hours until the solution becomes saturated. Saturation point is observed when further dissolution of calcium hydroxide powder will be ended. This solution is an alkali activated solution for rapid evaluation of pozzolanic activity by conductometric technique.
All solutions will be kept in a sealed container to prevent from carbonation and other contamination. The solutions to be used will be with less precipitate in order to avoid non- homogeneous properties of the testing solution.
Figure 3.4 Diagrammatic representation of Experimental set up.
3.6 Experimental Procedure for Conductivity Measurement.
200 ml of solution is taken in 250 ml conical flask with rubber cork, which is plugged in to avoid carbonation.
The electrical measuring equipments and magnetic stirrer with hot plate will be made available.
The required temperature will be set by adjusting hot plate's knob to attain the desired temperature of the solution.
After stabilizing temperature of solution, the required amount of Metakaolin will be added.1.0 grams of Metakaolin will be added in 200 ml of the solution.
The measurement of electrical conductivity will be started.
The variation of testing temperature will be controlled within ±1 degree of the testing temperature using magnetic stirrer.
The electrical conductivity of the solution at testing temperature will be recorded in terms of millisiemens per centimeter by using electrical conductivity meter.
The data will be fed to personal computer for analysis.
3.7 Correlation Analysis
Comparative studies will be made in this section considering several parameters of the tested pozzolans. The parameters studied are initial electrical conductivity, stabilized electrical conductivity and time period for stabilization of electrical conductivity.
Rate of change of conductivity of the suspension will be studied in regard to relation of compressive strength development of the pozzolan.
Normalized electrical conductivity is the ratio of electrical conductivity at any time to the initial conductivity of the solution. Inert material (river sand) will be used to check reduction in electrical conductivity with time. There is a need of adjustment to know the net reduction from the correction of electrical conductivity due to effect of pozzolan. The corrected reduction in normalized electrical conductivity will be normalized electrical conductivity of the inert material minus that of sample pozzolan. Normalized electrical conductivity with corrected reduction can be used as index in comparative studies to indicate reactivity of pozzolan.
Linear regressions will be used in this study to compare proposed technique with that of strength activity index. The correlation between the findings of the study and strength activity index will be determined.
The equation to be used is.
Whereas
y is results of strength activity index from the study,
x is parameter in the proposed technique in this study,
a and b are coefficients of regression.
And the determination coefficient (R2) will be calculated.
Table 3.3 Details of Experimental Program
S. No.
Metakaolin
No of specimens to be tested
Conductivity Measurement
Compressive Strength test (Days)
Suspension Temp. (°C)
Reaction Duration (Hr)
7
14
28
56
91
6
12
48
96
120
1
MK-L-40
MK-R-40
40
4
4
4
4
4
40
40
40
40
40
2
MK-L-50
MK-R-50
50
4
4
4
4
4
3
MK-L-60
MK-R-60
60
4
4
4
4
4
4
MK-L-70
MK-R-70
70
4
4
4
4
4
5
MK-L-80
MK-R-80
80
4
4
4
4
4
40
40
40
40
40
40
40
40
40
40
Total
400
Notes: Control= OPC Mortar; MK-L, MK-R =Metakaolin from Lampang and Ranong. Every groups of specimen includes the control sample.
3.5 Flow chart showing experimental procedure for conductivity measurement.
