Evaluation of Mechanical and Durability Performance of Fly Ash-Based Geopolymer Concrete

Abstract

Concrete usage around the world is second only after water. This work aims to reduce the usage of ordinary portland cement and to improve the usage of the other by products materials such as fly ash. The work in this study is divided in to four parts. The first part, trying different mix proportions of fly ash-based geopolymer concrete with many variables that effect on the compressive strength of fly ash -based geopolymer concrete. These variables were (water /geopolymer solid ratio, ratio of alkaline liquid /fly ash, sodium silicate solution/sodium hydroxide solution, concentration of sodium hydroxide, dosage of superplasticizer, rest period and temperature of curing ) in age (1, 3 and 28) days. Mechanical properties which include (compressive strength, splitting tensile strength, flexural strength, modulus of elasticity and bonding strength of the geopolymer concrete and its development with age (1, 3, 7, 28, and 56) day represent the second part. While the third part of this work include study the behaviour of durability of geopolymer concrete and comparison of results with normal concrete. Durability tests were (permeability, water absorption and sulphat resistance). Also studied the microstructure of the two types of concrete by using scanning electron microscopy (SEM) test and X-Ray diffraction (XRD), considered the fourth part. The results indicated that geopolymer concrete compressive strength effected by variables. Geopolymer concrete compressive strength decreases with increase of the ratio of water to geopolymer solid, dosage of superplasticizer. Geopolymer concrete compressive strength is increases with increasing the ratio of sodium silicate solution to sodium hydroxide solution, concentration of NaOH solution, rest period and curing temperature. Fly ash-based geopolymer concrete compressive strength higher than normal concrete at 7 days age by 1.4 times. That is mean fly ash -based geopolymer concrete compressive strength gain its strength at early age unlike normal strength concrete compressive strength. Fly ash–based geopolymer concrete shows good splitting tensile strength and flexural strength. Geopolymer concrete recorded good durability when comparing the results with normal concrete, it shows that GPC less permeability and water absorption than normal strength concrete by 64.6% and 38% respectively. Also GPC shows good resistance to sulphate attack, it was clear when residual compressive strength of geopolymer concrete was higher than normal strength concrete, it were 94.8% for geopolymer concrete and 85.5% for normal concrete. In addition to that SEM test results show difference in microstructure between geopolymer and normal concrete.