Abstract
In this study, the compressive strength and the permeation properties of fly ash-based Geopolymer were experimentally investigated. Type 2 Portland cement (T2PC) was partially or entirely replaced with 0, 10, 20, 30, 50, 70, and 100% of fly ash (FA). The laboratory tests were conducted for compressive strength at 7, 28, and 90 days, and permeation properties such as water absorption at 7 and 28 days. The main goal was to produce eco-friendly concrete with high strength and low permeability through blending cementitious materials including low Calcium (Ca) (T2PC and FA) for protecting concrete against sulphate attacks and other chemically destructive compounds in the environment. This study focused on the effectiveness of the curing period, combinations of chemical activators by varying the molarity of alkaline solutions between 4.16 and 12.96 M and keeping the sodium silicate (SS) to sodium hydroxide (SH) by the weight ratio of 2.5. Lab observations from this study demonstrated that the compressive strength was enhanced with the increment in fly ash content at all ages, with optimum being at 20% as the replacement of T2PC.
Highlights
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in Geopolymeric admixtures such as artificial pozzolans including fly ash (FA), silica fume (SF), and natural pozzolans including volcanic ash (VA) and opaline shade chert (OSC) as well as calcined diatomaceous earth (CDE) are partially used as the replacement of ordinary Portland cement (OPC) to improve the strength and durability of concrete so that these silicon or silicon-alumina materials containing activated silica and secondary cementitious properties do not exclusively have adhesive feature in the water, but that they react with calcium hydroxide released from the hydration process of Portland cement and
The compressive strength of low-calcium, FA-based geopolymer concrete was enhanced with the inclusion of FA as a replacement of Type 2 Portland cement (T2PC) up to 20% at all ages
The increment in concrete strength was observed due to additional calcium available in the chemical products formed by the hydration mechanism, which coexisted with the polymeric products of alumina-silicate
Summary
Geopolymeric admixtures such as artificial pozzolans including fly ash (FA), silica fume (SF), and natural pozzolans including volcanic ash (VA) and opaline shade chert (OSC) as well as calcined diatomaceous earth (CDE) are partially used as the replacement of ordinary Portland cement (OPC) to improve the strength and durability of concrete so that these silicon or silicon-alumina materials containing activated silica and secondary cementitious properties do not exclusively have adhesive feature in the water, but that they react with calcium hydroxide released from the hydration process of Portland cement and. It is worthwhile to state that the hydrated products achieved from the above-mentioned relations, Equations (4) and (5), have no notable role in the improvement of compressive strength in concrete It seems that the valuable compounds of Portland cement, C3 S and C2 S, have the most significant factor in the development of concrete strength so that the initial strength of concrete at early ages is because of the C3 S reaction and, subsequently, the acquisition of high strength in the weeks is due to the participation of C2 S in the hydration process. The sulphate attacks in concrete are accompanied by chemical reactions, which create the differential volume expansion in the hardened concrete, causing the compressive stresses, which are formed in several points of concrete in which the increment of these stresses leads to cracking and, eventually, failure in the concrete structure. Besides the use of compatible cement to neutralize the sulphate attacks, it is important to consider the water-to-cement (w/cm) ratio in a certain range, in which these supplementary limitations can increase the permeability of concrete in the adjacency of sulphate ion, resulting in the enhancement of concrete durability against environmental factors [14,15,16,17,18]
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