Strength Of Alkali-activated Slag Mortar Research Articles

Physico-mechanical properties and micromorphology of AAS mortars containing copper slag as fine aggregate at elevated temperature

Copper slag (CS) is an industrial by-product, which is commonly disposed in engineered landfills. Prior studies have successfully incorporated CS as an aggregate phase in cementitious materials. However, the alkali-activated material (AAM) incorporating CS has been scarcely studied. Specifically, the elevated temperature behavior of AAM with CS has not been investigated previously. The present paper aims to study the effects of elevated temperature treatment on the mass loss and residual strength of alkali-activated slag mortars incorporating 0–100% (by volume) of CS with an incremental step of 20% instead of natural sand. The mass loss, compressive and flexural strengths, and microstructure of the mixes before and after exposure to temperatures of 25, 200, 400, 600, and 800 °C were evaluated and compared. Results showed that the optimum performance of the mortar at elevated temperatures is achieved by incorporating 20% CS. It led to 24% higher mechanical strength at 800 °C than the reference mix. However, mixes with CS content beyond 60% showed inferior mechanical strength at elevated temperatures in comparison to the control mortar. The optimum mortar exhibited improvement in microstructure's density and less micro-cracking based on the results of scanning electron microscopy (SEM) analysis. Finally, the mortar mixes made with CS as fine aggregate were also established to be environmental-friendly and cost-efficient.

Early-Age Strength of Alkali-Activated Slag Mortar Based on Burned Oyster Shell and Other Chemical Activators

AbstractAn alkaline-activated, ground-granulated blast furnace slag (BFS) was used as a binder for mortar prepared using river sand. Sixteen mortar mixes with four different BFS:sand ratios (4%, 8%...

Effect of Heat Curing Method on the Mechanical Strength of Alkali-Activated Slag Mortar after High-Temperature Exposure

The aim of this work was to study the mechanical strength and microstructure changes of alkali-activated slag mortar (AAS mortar) after being heat treated in the temperature range of 200–1000 °C. The AAS mortar was cured in the ambient condition (20 ± 5 °C, 60 ± 5% RH) (Relative humidity: RH) and high temperature condition (80 °C) for 27 days with three different heating regimes: curing in a dry oven, curing in sealed plastic bags, and in a steam environment. The activator for the AAS synthesis was a mixture of sodium silicate solution (water glass) and sodium hydroxide (NaOH) with a SiO2/Na2O weight ratio of 1, and a dosage of 4% Na2O by slag weight. Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) incorporated with energy-dispersive X-ray spectroscopy (EDX) were used to assess the mortar microstructure change. The results revealed that the curing method significantly affected the mechanical strength of AAS at temperatures lower than 800 °C. The heat treatment at late age of 28 days was more beneficial for compressive strength enhancement in specimens without using heat curing methods.

Influence of activator on the strength and drying shrinkage of alkali-activated slag mortar

The development of new binders, as an alternative to traditional cement, by the alkaline activation of industrial by-products (i.e. ground granulated slag and fly ash) is an ongoing research topic in the scientific community [Puertas F, Amat T, Jimenez AF, Vazquez T. Mechanical and durable behaviour of alkaline cement mortars reinforced with polypropylene fibres. Cem Concr Res 2003;33(12): 2031–6]. The aim of this study was to investigate the feasibility of using and alkaline activated ground Turkish slag to produce a mortar without Portland cement (PC). Following the characterization of the slag, mortar specimens made with alkali-activated slag were prepared. Three different activators were used: liquid sodium silicate (LSS), sodium hydroxide (SH) and sodium carbonate (SC) at different sodium concentrations. Compressive and flexural tensile strength of alkali-activated slag mortar was measured at 7-days, 28-days and 3-months. Drying shrinkage of the mortar was measured up to 6-months. Setting times of the alkali-activated slag paste and PC paste were also measured. Setting times of LSS and SH activated slag pastes were found to be much slower than the setting time of PC paste. However, slag paste activated with SC showed similar setting properties to PC paste. LSS, SH and SC activated slag mortar developed 81, 29, and 36 MPa maximum compressive strengths, and 6.8, 3.8, and 5.3 MPa maximum flexural tensile strengths at 28-days. PC mortar developed 33 MPa compressive strength and 5.2 MPa flexural tensile strength. LSS and SH activated slag mortars were found to be more brittle than SC activated slag and PC mortars. Slag mortar made with LSS had a high drying shrinkage, up to six times that of PC mortar. Similarly, slag mortar made with SH had a shrinkage up to three times that of PC mortar. However, SC activated slag mortar had a lower or comparable shrinkage to PC mortar. Therefore, the use of SC as an activator for slag mortar is recommended, since it results in adequate strength, similar setting times to PC mortar and comparable or lower shrinkage.