Factors affecting the slump and strength development of geopolymer concrete

Abstract

Cement production is estimated to be responsible for 5-8% of global total carbon dioxide (CO2) emissions. Geopolymer concrete (GC) is claimed to release up to 45% less CO2 for a comparable concrete, but is more difficult to manufacture. This study investigated the effect of factors other than mix design on the slump and strength development of GC produced from low-calcium fly ash (FA) and up to 50% ground granulated blastfurnace slag (GGBS) replacement; these were: curing methods and temperatures (at 10, 20 and 75 o C); FA fineness; superplasticiser type; water content; and GGBS/FA ratio. Methods are also presented for the volume-to-mass conversion of sodium hydroxide at a specific molarity and ambient temperature, and an effective combination of wax-based mixtures as mould agents to overcome the inherent manufacturing mould release difficulties. Steam-curing improved the compressive strength of the FA-based GC over oven drying by up to 20%, as did increasing the FA fineness (although this became negligible with 50% GGBS replacement). Both naphthalene and polycarboxylate superplasticizers improved the slump of GC (from 110 to 210 mm) without significantly reducing the compressive strength (< 5 MPa). Water content of GC had a great 2 effect on the slump, but less so on the compressive strength. Increasing the GGBS content gradually decreased the slump but rapidly increased the strength, regardless of the curing temperatures of 20 or o C. The GC with the minimum of 20% GGBS replacement achieved 33 MPa after 28 days curing at 10 o C. Air-dry curing provided a greater strength development of FA-based GC than water curing, though the opposite was observed for the 50/50 GGBS/FA GC. Consideration of these factors can significantly ease the manufacture of GC, enhancing its potential application in real structures, and consequently helping reduce global (CO2) emissions.

Survey of Mechanical Properties of Geopolymer Concrete: A Comprehensive Review and Data Analysis

“…According to Nguyen et al [ 2 ], increasing water/solid ratio from 0.2 to 0.3, can decrease the compressive strength of the FA-based GPC for alkaline-to-binder ratios of 0.3 and 0.4, while tests by Ahmad [ 59 ] for GPC subjected to initial curing at 70 °C (Oven) for 24 h showed that the optimum water/binder ratio is 0.25 to obtain maximum compressive strength. There was a strength increase with increasing alkali/fly ash ratio up to 0.45, lower than 0.5 measured by Al Bakri et al [ 60 ] and Abdullah et al [ 50 ].…”

“…The superiority of slag on fly ash for GPC subjected to different curing regimes was also observed by Kurtoğlu et al [ 78 ]. Other tests showed that replacement of fly ash by GGBS up to 30% leads to an increase in compressive strength regardless of the curing temperature [ 2 ]. On the other hand, Yunsheng et al [ 27 ] and Abhilash et al [ 79 ] reported that the maximum compressive strength is related to replacing 50% metakaolin with GGBS.…”

“…Instead, there is an alkali-activated mineral admixture as a binding medium holding an inert aggregate to form a compact mass. This new type of concrete can offer many benefits including high early strength [ 2 ], high temperature resistance [ 3 ], and good chemical resistance for aggressive environments [ 4 ], as compared with normal concrete. In particular, durability of ordinary Portland cement concrete is under examination, as many concrete structures, especially those built in corrosive environments, start to deteriorate after 20 to 30 years [ 5 ].…”

Geopolymers and Fiber-Reinforced Concrete Composites in Civil Engineering

“…Many factors that affect the compressive strength, flexural strength and other mechanical properties of geopolymers have been reported by different researchers [ 22 , 38 , 39 , 40 , 41 , 42 ]. These factor, such as different calcium-containing raw materials [ 21 , 43 ], ionic additives, curing procedures and post-curing chemical treatment, have been considered important for final properties [ 44 , 45 , 46 ]. An amorphous structure of geopolymers is better for realizing anticipated mechanical strength.…”

Studi Eksperimental Pengaruh Sudut Kemiringan Penyambungan Balok Beton dengan Bondcrete Terhadap Kuat Lentur Beton

“…Setelah proses pencampuran beton selesai, maka diperlukan pengujian beton segar. Pengujian beton segar dilakukan untuk mengetahui kekentalan beton yang berpengaruh terhadap kemudahan pengerjaan (workability) dan homogenitas dari campuran beton (Nguyen et al, 2020). Pada penelitian ini dilakukan pengujian beton segar dengan slump test.…”