A STUDY ON THE PERFORMANCE AND BOND BEHAVIOUR OF HIGH STRENGTH GEOPOLYMER CONCRETE

Abstract

Geopolymer concrete (GPC) is a promising alternative to ordinary Portland cement (OPC), offering significant solutions to the issues of CO2 emissions from cement production and the utilization of industrial byproducts. Rapid urbanization created a demand for high-rise structures, necessitating the use of high-strength concrete. In the present investigation, High Strength Geopolymer Concrete (HSGPC) cured at ambient temperature is developed using particle packing concepts and multicomponent binder system. Also, investigated its strength properties along with resistance against chemical attack. The main aim of this work is to study the bond behaviour of HSGPC. In the present investigation, the experimental bond behaviour is determined through pullout and hinged beam tests. Finite element-based software ATENA V5.7.0p has been used to predict the bond behaviour of HSGPC. The work is carried out in four different phases as described below. Phase-I Particle packing methods MTM and JDD are adopted to optimize the aggregate proportions. Binders such as flyash, GGBS, silica fume, alccofine, and OPC are used to develop high strength geopolymer concrete. The mechanical characteristics such as compressive strength, flexural strength, and splitting tensile strength are determined as per IS 516: 2004. The modulus of elasticity and stress-strain behaviour is determined as per ASTM C469-02. Based on the experimental results, analytical models for the prediction of mechanical characteristics are proposed. A constitutional model for the prediction of stress-strain behaviour of HSGPC is included in the study. The influence of binder materials on microstructure properties is examined through microstructure characterization techniques such as SEM, XRD, FT-IR, EDS, and BSE. Phase-II The chemical resistance of high-strength GPC (60, 80 and 100 MPa) is investigated by exposing the specimens to HCl, H2SO4, MgSO4, and NaCl. Parameters such as Dimension Loss Factor (DLF), Mass Loss Factor (MLF), Strength Loss Factor (SLF) and thus Acid Durability Loss Factor (ADLF) are evaluated. Rebound number and ultra-sonic pulse velocity assessment is done on the specimen before and after chemical exposure. vii Phase-III One of the important structural parameters, the bond behaviour of HSGPC is determined through the anchorage and flexural bond test. The anchorage bond behaviour is determined by employing the pullout test, while the flexural bond behaviour is determined by employing the hinged beam test. The pullout bond behaviour is determined by considering parameters such as bar diameter (12, 16, and 20 mm), embedment length (2.5D, 5D, and full depth), and grade of concrete (60, 80, and 100 MPa). The flexural bond behaviour is determined by considering parameters such as cover to concrete (16, 20, and 40 mm), bar diameter (12, 16, and 20 mm), and grade of concrete (60, 80, and 100 MPa). The pullout test is performed according to IS 2770: Part 1 and flexural bond behaviour is determined according to Rilem Feb ceb (1982) RC5-TC9. Phase-IV The experimental bond behaviour of geopolymer concrete studied in Phase III is used to validate the numerical results from finite element software ATENA. Also, the parametric study is extended by considering variables such as type of bar (plain and ribbed), bar diameter (10, 12, 16 and 20 mm), embedment length (50, 75 and 100 for 10 mm and 12 mm bar diameter, 50, 75, 100 and 150 mm for 16- and 20- mm bar diameter) and compressive strength of concrete (20, 30, 40, 50, 60, 70, 80, 90, and 100 MPa) under pullout test. Also, the parameters like the ratio of embedment length to bar diameter (3, 5, 7, 9) and cover to bar diameter (1 to 5 at an increment of 0.5), compressive strength of concrete (20, 30, 40, 50, 60, 70, 80, 90, and 100 MPa) are considered for determining the flexural bond strength using beam end test. Based on the experimental and numerical analysis it was concluded that there is a significant improvement in the microstructure and mechanical properties of HSGPC with the utilization of multi-component binders and particle packing models. The addition of alccofine in GPC mixes increased the compressive, splitting tensile and flexural strength of concrete. HSGPC of compressive strength 100 MPa was achieved at room temperature curing. From the microstructure analysis of GPC, it was noted that the addition of alccofine and silica fume increased the percentage of Ca bonds along with the Si bonds which led to dense microstructure attributed to polymerization and polycondensation. Analytical models for the prediction of modulus of elasticity, splitting, and flexural strength along with a constitutive model for the prediction of stress-strain behaviour of HSGPC is proposed. For an exposure period of 90 days of HCl, H2SO4, MgSO4, and NaCl, 60 MPa concrete showed the highest chemical resistance viii compared to 80 and 100 MPa by exhibiting lower loss factors, indicating that a higher percentage of siliceous compounds than calcium compounds increase the resistance of concrete to acid, sulfate and chloride attack. Pullout and flexural bond strength increased with an increase in the grade of concrete and decreased with an increase in bar diameter and embedment length. With the increase in cover concrete, the flexural bond strength has improved. Similarly, the slip corresponding to maximum bond stress decreased with increase in compressive strength, bar diameter, embedment length and cover to concrete. Based on the numerical analysis, analytical models for the prediction of bond behaviour of normal, standard and high-strength GPC are proposed. The proposed analytical models are compared with the available models in the literature and existing standards.