CHAPTER-3 MIX DESIGN AND STRENGTH PROPERTIES OF GPC

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1 65 CHAPTER-3 MIX DESIGN AND STRENGTH PROPERTIES OF GPC 3.0 IMPORTANCE OF MIX DESIGN Many parameters are involved in the production of GPC, out of which alkaline liquid mineral admixtures ratio and superplasticiser are important. Sulphonated Naphthalene based dispersing agents are adopted as super plasticizers to obtain better mechanical properties of GPC. Low calcium flyash gives better results from the point of view of chemical composition. GGBS is used to fill the voids between flyash and fine aggregate and this helps in the degree of particle aggregation, nature and quantity of impurities and basic particle size. Sodium hydroxide and sodium silicate solutions used as alkaline liquids react with flyash and GGBS to form the geopolymer gel binding the aggregates to produce GPC. The final product was cured in steam curing chamber at 60 C for 24 hours. Based on review of literature, Rangan s method [18] has been adopted to produce M60 GPC. TVC mix design has been carried out using Perumal s method [112]. 3.1 MATERIALS CHARACTERISTICS Fly Ash Fly ash is the alumino silicate source material used for the synthesis of geopolymeric binder. Class F fly ash shown in fig 3.1 obtained from the silos of Raichur Thermal Power Station, Karnataka

2 66 was used for the experimental work. The percentage of fly ash passing through 45µm IS Sieve was found to be 95%. The physical characteristics are as shown in table 3.1 Fig Low calcium Fly Ash (ASTM Class F) Table Physical Characteristics of Fly Ash Properties Values Specific gravity 2.40 Blaine s fineness (m 2 / kg) Ground granulated blast furnace slag Ground Granulated Blast Furnace Slag (GGBS) shown in fig 3.2 is a byproduct of the steel industry. Blast furnace slag is defined as the non-metallic product consisting essentially of calcium silicates and other bases that is developed in a molten condition simultaneously with iron in a blast furnace. About 10% by mass of binders was replaced with GGBS. Fig Ground Granulated Blast Furnace Slag (GGBS)

3 67 Sieve size (mm) Coarse and Fine Aggregates The fine aggregate used in the study was river sand and coarse aggregate are crushed angular granite stone passing 12.5 mm sieve. The sieve analysis of fine and coarse aggregate are shown in table 3.2 & 3.3 Wt. retained (gms) Table Sieve Analysis Results of Fine Aggregate Cum. % Wt. retained % Wt. passing Specifications as per IS 383: 1993 [133] for % passing with different zones I II III IV Sl. No Table Sieve Analysis Results of Coarse Aggregate Sieve Size (mm) Wt. Retained % Wt. Retained Cum. % Wt. Retained % Wt passing Grading limits as per IS 383: 1993 [133] Coarse and fine aggregate tested conforms to the specifications as per IS 383: 1970 [110] with fine aggregate belonging to zone II as per the specifications. The physical characteristics of coarse and fine aggregates are shown in table 3.4 and 3.5 Table Physical Characteristics of Coarse Aggregates Specific Fineness Flakiness Density (kg/m Sl. No. 3 ) Gravity Modulus Index Loose Rodded %

4 68 Table Physical characteristics of Fine Aggregates Specific Fineness Flakiness Density (kg/m Sl. No. 3 ) Gravity Modulus Index Loose Rodded % Alkaline Liquids Sodium silicate gel (Na2SiO3) and sodium hydroxide (NaOH) solutions used for fly ash activation is shown in fig 3.3 Sodium hydroxide solution of 8, 12 and 14 Molar was prepared by mixing the pellets with water. The mass of NaOH solids in a solution varied depending on the concentration of the solution expressed in terms of molar, M. For instance, NaOH solution with a concentration of 8M consisted of 8 40 = 320 grams of NaOH solids (in pellet form) per litre of the solution, where 40 is the molecular weight of NaOH. The Sodium silicate and Sodium hydroxide solution were mixed 24hrs prior to usage. Fig Sodium hydroxide pellets and Sodium silicate solution Super plasticizer Super plasticizers are capable of reducing water contents by about 30 percent. However it is to be noted that full efficiency of super plasticizer can be got only when it is added to a mix that has as initial slump of 20 to 30 mm. Addition of super plasticizer to stiff concrete mix reduces its water reducing efficiency. Depending on the solid content of

5 69 the mix, a dosage of 1 to 3 percent by weight is recommended. For the present investigation, a super plasticizer namely CONPLAST SP 430 has been used for obtaining workable concrete at low a/m ratio. CONPLAST SP 430 complies with IS 9103: 1999 [130] and BS: 5075 part 3 and ASTM C 494, TYPE B as a HR WRA. CONPLAST SP 430 is based on Sulphonated naphthalene formaldehyde (NSF) condensates with chloride content Water Potable drinking water was used. 3.2 NORMAL CONCRETE Cement The cement used in the study is ordinary Portland cement (53 Grade) conforming to IS 12269: 1987 [131] with the physical characteristics as shown in table Silica fume Table Physical Characteristics of Cement Properties Values Specific gravity 3.07 Blaine s fineness (m 2 / kg) 310 Silica fume is a by-product of silicon metal or ferrosilicon alloy production. 42 kg/m 3 of silica fumes was used in M60 concrete.

6 GPC MIX DESIGN AND EXPERIMENTAL DATA Ingredients Required The range of ingredients for M60 concrete based on Rangan s [18] Is listed below. Fly ash Low calcium (ASTM Class F) GGBS 10% of flyash Ratio of Na2SiO3 Solution to NaOH Solution, by mass 0.4 to 2.5 Molarity of NaOH Soln 8M to 14M. Alkaline liquid to Binders ratio 0.3 and Aggregates Super plasticizer 75 to 80% of mass of concrete 2.5 to 3% of flyash and GGBS GPC mix design based on trial mix design and the following quantities are arrived for M60 concrete as given in table MIX DESIGN FOR TRADITIONALLY VIBRATED CONCRETE PROCEDURE Target Mean Strength Target mean strength is calculated as follows: = fck + (t s) with usual IS notations. When adequate data are not available to establish, the fck value can be determined from the following table 3.7 given by ACI report 318.

7 71 Table Target Mean Strength when Data are not available to establish a Standard Deviation Specified Characteristic Compressive Strength, fck (MPa) Less than More than 34.5 Target mean Compressive Strength, (MPa) fck fck fck Selection of maximum size of coarse aggregate The maximum size of the coarse aggregate is selected from the following table 3.8 as given by ACI Report 211.4R.93. Table Maximum Size of Coarse Aggregate Characteristic Comp. Strength, fck (MPa) Less than 62 Greater than or equal to 62 Maximum aggregate size (mm) Estimation of free water content The water content to obtain the desired workability depends upon the quantity of water and super plasticizer. However, the saturation point of the super plasticizer is known, and then the water dosage is obtained from the following table 3.9 If the saturation point is not known, it is suggested that a water content of 150 liters/m 3 shall be taken to start with. Table Determination of the Minimum Water Dosage Saturation Point (%) Water (l/m 3 )

8 Super plasticizer dosage The super plasticizer dosage is obtained from the dosage at the saturation point. If the saturation point is not known, it is suggested that a trial dosage of 1.0% shall be taken to start with Estimation of air content The air content (approximate amount of entrapped air) is obtained from the table 3.10 as given ACI Report 311.4R.93. However, it is suggested that an initial estimate of entrapped air content shall be taken as 1.5% or less, and then adjusting it on the basis of the result obtained with the trial mix. Table Approximate Entrapped Air Content Nominal maximum size of Coarse aggregate (mm) Entrapped air, as percent of Volume of concrete Selection of coarse aggregate content The coarse aggregate content is obtained from the table 3.11 as a function of the particle shape. If there is any doubt about the shape of the CA or if its shape is not known, it is suggested that a CA content of 1050 kg/m 3 shall be taken to start with. The CA so selected should satisfy the requirements of grading and other requirements of IS 383: 1970 [110].

9 73 Table Coarse Aggregate Content CA Particle shape CA Dosage (kg/m 3 ) Elongated or Flat Average Cubic Rounded Selection of water-binder ratio The water-binder ratio for the target mean compressive strength is chosen from fig 3.4, the proposed w/b ratio Vs compressive strength relationship. The w/b ratio so chosen is checked against the limiting w/c ratio for the requirements of durability as per table 3.5 of IS 456: 2000 [132] and the lower of the two values is adopted. Fig w/b ratio v/s compressive strength relationship Calculation of binder contents The binder or cementitious contents per m 3 of concrete is calculated from the w/b ratio and the quantity of water content per m 3 of concrete. The cement content so calculated is checked against the minimum cement content for the requirements of durability as per table and of IS 456: 2000 [132] and the greater of the two values is adopted.

10 Estimation of fine aggregate content The absolute volume of FA is obtained from the following equation: Vfa = [Vw + (Mc/ Sc) + (Msf/ Ssf) + (Mca / Sca) + Vsol + Vea] Where, Vfa = absolute volume of FA in liters per m 3 of concrete Vw = volume of water (liters) per m 3 of concrete Mc = mass of cement (kg) per m 3 of concrete Sc = specific gravity of cement Msf, Mca = Total masses of the SF and CA (kg) per m 3 of concrete respectively Sca, Ssf = specific gravities of saturated surface dry coarse aggregate and silica fume respectively, and Vea = Volume of the entrapped air (liters) per m 3 of concrete respectively. The fine aggregate content per unit volume of concrete is obtained by multiplying the absolute volume of fine aggregate and the specific gravity of the fine aggregate Moisture Adjustments The actual quantities of CA, FA and water content are calculated after allowing necessary corrections for water absorption and free (surface) moisture content of aggregates. The volume of water included in the liquid super plasticizer is calculated and subtracted from the initial mixing water.

11 Unit Mass of Concrete The mass of concrete per unit volume was calculated by adding the masses of the concrete ingredients. Trial mixes were done to obtain mixes having suitable consistency and workability. The results of the trials are indicated in table 3.12 for GPC mix 2 was adopted and the final proportions for M60 is indicated in table 3.13 (GPC and TVC). Table Trial Mixes (GPC) Mass, kg/m 3 Materials Mix1, Mix2, Mix3, Mix4, Al/Fa=0.3 Al/Fa=0.35 Al/Fa=0.4 Al/Fa=0.45 Coarse aggregates Fine sand Fly ash GGBS Na2SiO3 solution NaOH solution Super plasticizer 3% 3% 3% 3% Extra water 3% 3% 3% 3% Table Mix proportion for M60 concretes Materials GPC TVC Cement kg/m Fly ash kg/m GGBS kg/m Silica fume kg/m 3-42 Coarse aggregate kg/m Fine aggregate kg/m NaOH solution (8M) kg/m Na2SiO3 solution kg/m Water l/m Super plasticizer (%) The present investigation shows that high strength GPC mix proportioning can be done on similar guide lines given by Rangan s method. Further investigations are to be carried out to validate the

12 76 author investigation for generality of the Rangan s method for all grades of geopolymer concrete. 3.5 PRODUCTION METHODOLOGY Introduction Fly ash-based geopolymer concrete using low calcium (ASTM Class F) requires trial and error process was used. The focus of the study is to identify the salient parameters that influence the mix proportions and the properties of GPC. The current practice used in the manufacture and testing of TVC was followed. In order to simplify the development process compressive strength is selected as the benchmark parameter. This is not unusual because compressive strength has an intrinsic importance in the structural design of concrete structures Materials for GPC and TVC The material for GPC and TVC described in article SPECIMEN PREPARATION Six cubical moulds of size 100mm, six cylindrical moulds of size mm and six prisms of size mm were used to prepare specimen of GPC and TVC. 3.7 MIXING Geopolymer Concrete Fly ash, GGBS and aggregates were mixed dry in the 100 kg capacity pan mixer for 3 minutes. The alkaline solution that was

13 77 prepared one day prior with super plasticizer and extra water were added into the blend and mixed for 4 minutes Test on Fresh Concrete The fresh fly ash-based geopolymer concrete was light in colour and shiny in appearance (fig 3.5). The mixtures were usually cohesive. The workability of both geopolymer and traditionally vibrated concrete were measured by means of the conventional slump test. Fig Slump test on fresh concrete to assess the workability Casting The fresh concrete was then cast into standard cylindrical moulds, cubes and prisms, which was compacted using vibrating table are shown in figs 3.6 to 3.8 Fig Concrete being poured to a tray Fig Moulds on vibrating table

14 78 Fig Concrete in moulds after compaction Curing After demoulding GPC specimens were then transferred to a steam curing chamber, having a temperature of 60 C inside the chamber for 24 hours. A boiler was used to produce the steam, which was let in to the chamber (fig 3.9). At the end of the curing regime, the specimens were allowed to cool in air, kept in open till the day of testing. TVC specimens were demoulded after 24 hours and cured in water pond till the day of testing. Fig Steam Boiler with curing chamber

15 STRENGTH STUDIES Compressive Strength The GPC and TVC specimens were tested for 7, 14 and 28 days compressive strength as per IS 516: 1959 [127]. The specimens were cleaned and weight of each specimen were recorded. After which the specimen was kept in compression testing machine and loaded till fail as shown in fig 3.10 Fig Specimens before and after compression testing Split Tensile Strength The GPC and TVC cylindrical specimens were tested for 28 days split tensile strength as per IS 5816: 1999 [128] using compression testing machine. The test consists of applying compressive line loads along the opposite generators of a concrete cylinder placed with its axis horizontal between the plattens as shown in fig 3.11 The magnitude of the tensile stress is given by 2P/πDL, where P is the applied load causing splitting of the specimen, where D and L are the diameter and length of the cylinder respectively.

16 80 Fig Specimens before and after split tensile testing Flexure The GPC and TVC specimens were tested for 28 days flexure strength with the modulus of rupture is determined by testing test specimens of mm prism as shown in fig 3.12 The modulus of rupture is determined from the equation fr = M/Z. where M is the bending moment causing the flexure failure and Z is the sectional modulus. Fig Specimen before and after flexural testing 3.9 COMPARISON OF STRENGTH PROPERTIES - GPC AND TVC Compressive strength For M60 grade concrete the compressive strength results of both GPC and TVC are tabulated in the table 3.14

17 81 Table Compressive strengths for GPC and TVC Split tensile strength Days GPC (MPa) TVC (MPa) For M60 grade concrete the split tensile strength results of both GPC and TVC are tabulated in the tables 3.15 & 3.16 Table Split tensile strength values GPC Tensile load (kn) Splitting tensile strength (MPa) Average 3.55 Table Split tensile strength values TVC Tensile load (kn) Splitting tensile strength (MPa) Average Flexural strength For M60 grade concrete the flexural strength results of both GPC and TVC are tabulated in the tables 3.17 & 3.18 according to IS 456 [132].

18 82 Table Flexural strength values for GPC Mix no DG reading P (N) f = Pl/bD Average MPa MPa Table Flexural strength values for TVC Mix no DG reading P (N) f = Pl/bD Average MPa MPa 3.10 CONCLUSIONS OF STRENGTH PROPERTIES OF M60 GPC AND TVC Compressive strength GPC is around 62% more than OPC in 7 days but at 28 days the strength difference between GPC and TVC is only 5%. Hence GPC is attaining early strength but the improvement of strength after 7days is less Split Tensile Strength Tensile strength of GPC is 20% less than TVC. Rapid development of tensile strength is achieved.

19 83 It is true that geopolymer concrete which performs better in compressive strength should have performed in a better way also in split tensile strength as available in the literature. More tests are required to throw light on this so that split tensile strength can be correlated with the corresponding compressive strength Flexural strength There is no much variation in experimental and theoretical values of flexural stress. There was no much difference found in Flexural stresses of GPC and TVC.