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The shear, flexural and axial tensile bond strengths of alkali-activated slag concrete hollow block (AASCHB) masonry layered with alkali-activated slag (AAS) mortar were investigated in this study. A comprehensive experimental investigation was conducted to assess the effect of the AAS mortar strength on the bond characteristics of the masonry. The bond strength of the AASCHB masonry was found to be directly related to the compressive strength of the AAS mortar, where higher compressive strength led to higher bond strength. In addition, new expressions for the bond strength were developed for AASCHB masonry based on the compressive strength of AAS mortar.

Recently, alkali-activated slag mortars have attracted considerable attention as environmentally friendly materials. The objective of this paper was to explore the influence of an alkaline activator (NaOH or NaOH/Na2CO3 solutions) on the performance of alkali-activated slag (AAS) mortars with pottery sand as fine aggregate. Five Na2CO3-to-NaOH ratios of 0/100, 20/80, 40/60, 60/40, and 80/20, and three Na2O contents of 4%, 6%, and 8%, were used to prepare AAS mortars. The water-to-slag ratio and slag-to-aggregate ratio were kept constant, at 0.38 and 0.8, respectively. The setting time, fluidity, compressive strength, and drying shrinkage were measured. The reaction hydrates were analyzed using microscopy and elemental analysis, while the pore structures were characterized using mercury intrusion porosimetry. The experimental results showed that both the Na2CO3-to-NaOH ratio and Na2O content had a significant effect on the fresh and hardened properties of AAS mortars. A high Na2CO3-to-NaOH ratio and low Na2O content resulted in AAS mortars with longer initial and final setting times. The higher Na2CO3-to-NaOH ratios led to a higher late compressive strength of AAS mortars, where the 6% Na2O samples showed the best performance with Na2O contents of 4–8%. In addition, the drying shrinkage behavior of AAS mortars as a function of Na2CO3-to-NaOH ratio was dependent on the Na2O content. Moreover, the compressive strength and drying shrinkage have a direct relationship with the microstructure of AAS mortars.

This study focused on the engineering properties of alkali-activated slag (AAS) pastes prepared by mixing an activator consisting of sodium silicate and sodium hydroxide at room temperature. The water-to-slag ratio of AAS paste was kept constant at 0.35 by mass. AAS pastes were prepared using the activator with five different silicate moduli of 1, 1.2, 1.4, 1.6, and 1.8 and three different Na2O contents of 6%, 8%, and 10%. The results showed that both the silicate moduli and Na2O contents had significant effects on the engineering properties of AAS pastes. All the AAS pastes exhibited properties such as fast setting, good workability, and high early compressive strength. The final setting time varied from 9 to 36 min, and the fluidity was in the range of 147–226 mm. The 1 d compressive strength of all the AAS pastes, which could be easily achieved, had values above 55 MPa, whereas the highest strength obtained was 102 MPa with the silicate modulus of 1 and Na2O content of 8% at room temperature. The drying shrinkage increased as the silicate modulus increased. Furthermore, the hydration products and microstructures of AAS pastes were explained according to the microanalysis methods.

This study investigated the properties of alkali-activated slag (AAS) pastes with NaOH and a blend of NaOH and Na2CO3 as the alkaline activator. The effects of five different Na2CO3 to NaOH molar ratios (0:10, 0.9:10, 2.5:10, 5.7:10 and 15:10) and three different Na2O contents (4%, 6% and 8%) in the alkaline activator on the setting time, mechanical performance and drying shrinkage were tested. The water to slag ratio was 0.35 by weight. The results showed that both the Na2CO3 to NaOH molar ratios and Na2O contents are major factors influencing the fresh and hardened pastes. Higher Na2CO3 to NaOH molar ratios yielded a longer setting time and higher compressive strength. The Na2O content of 6% was more sensitive to the properties compared with 4% and 8% Na2O. When the Na2O content was 4%, the drying shrinkage increased as the Na2CO3 to NaOH molar ratio increased; however, when the Na2O content increased to 6% and 8%, the drying shrinkage decreased as the Na2CO3 to NaOH molar ratio increased. The main hydration products were C-S-H(I), hydrotalcite, calcite and gaylussite. There was a strong relationship between the drying shrinkage and pore structures of AAS. Consequently, the Na2CO3 to NaOH molar ratio of 15:10 and Na2O content of 6% can be regarded as the optimum mix proportion.

This study focused on the effects of curing conditions (standard and steam curing) on the freeze–thaw resistance of geopolymer mortars containing Class C fly ash, Class F fly ash, slag, and Ca(OH)2. Geopolymer mortar specimens were prepared with water-to-Class C fly ash ratios of 0.35 and 0.40, and CaO contents of 45% and 100% with different compositions. The specimens were subjected to freeze–thaw cycles until the mass loss exceeded 5% or the relative dynamic elastic modulus was below 60%. The reaction hydrates and pore structures were analyzed using scanning electron microscopy with energy-dispersive spectrometry and mercury intrusion porosimetry, respectively. In terms of mechanical performance, steam curing condition was better than standard curing condition for the early-age strength of geopolymer mortars. The compressive strength of the geopolymer mortars at 2 d and 28 d was increased 2.2–5.1 times and 0%-40%, respectively, under steam curing condition compared with standard curing condition. The experimental results indicated that Class C fly ash geopolymer mortar (CF35) under steam curing condition and Class F fly ash-slag geopolymer mortar with 100% CaO content (SF35C100) under standard curing condition exhibited remarkable freeze–thaw resistance with a freeze–thaw resistance grade of F300 at the lowest. Moreover, the water-to-ash ratio was critical for the freeze–thaw resistance under both standard and steam-curing conditions. The mass loss of specimens with water-to-ash ratios of 0.35 and 0.40 under standard curing condition were 4.67% and 8.79%, respectively, at 25 freeze–thaw cycles, whereas that of specimens with water-to-ash of 0.35 under steam curing condition was 3.03% at 300 freeze–thaw cycles. In addition, the freeze–thaw resistance of geopolymer specimens with different compositions had a direct relationship with the microstructure of the geopolymer mortars. Furthermore, the experimental results verified that a higher compressive strength did not necessarily indicate a better freeze–thaw resistance.

In this paper, a parametric experimental study developing the alkali-activated slag concrete hollow block (AASCHB) is discussed. Fourteen trial mixes of alkali-activated slag concrete containing pottery sand and ceramsite with different water-to-slag ratios, sand ratios, silicate moduli, and Na2O contents were evaluated to determine the optimal mix for high compressive strength and low drying shrinkage. All four factors evaluated were found to be significant for the desired properties. A series of 390 &times, 190 &times, 190 mm3 AASCHBs were prepared using the optimal mix with a water-to-slag ratio of 0.35, sand ratio of 0.64, silicate modulus of 1.2, and Na2O content of 8%. The compressive strength, flexural strength, water absorption, and moisture content tests of these blocks indicate that the resulting AASCHB can be classified under the strength grade of MU15 as a load-bearing hollow concrete block. The proposed AASCHBs appear to provide a viable solution to the environmental problems of industrial waste and cement production emissions, leading to more sustainable buildings without compromising structural performance.

Alkali-activated slag (AAS) mortars were prepared using pottery sand as a fine aggregate in a ratio of 1 : 1.75 using a blend of sodium silicate and NaOH as an alkaline activator at room temperature. The effects of sodium oxide content and silicate moduli on the setting time, fluidity, consistency, compressive strength, and drying shrinkage of different AAS mortars were determined. These results revealed that sodium oxide content and silicate modulus had little effect on the setting time and workability of the mortar; however, they did have a significant effect on their mechanical performance and drying shrinkage levels. All the AAS mortars exhibited faster setting times, better workability, and higher early and late compressive strength compared to traditional mortars. Optimum compressive strength was achieved at 93 and 123 MPa after 1 d and 28 d, respectively, using a silicate modulus of 1.2 and Na2O content of 8%. The microstructures of mortars were characterized using scanning electron microscopy with energy dispersive spectrometric (SEM/EDS) and mercury intrusion porosimetry (MIP). These results reveal that AAS mortars containing pottery sand as a fine aggregate may represent a promising building material with improved properties for use in the construction industry.

This paper investigated the curing effects on the mechanical properties of calcium-containing geopolymer mortar. Three precursors are used: Class C fly ash, Class F fly ash plus calcium hydroxide and Class F fly ash plus slag. Curing conditions included: (1) standard curing at 20 ± 3 °C and RH 95% (C); (2) steam curing at 60 °C for 24 h (S); (3) steam curing at 60 °C for 6 h (S6); and (4) oven curing at 60 °C for 24 h (O), then the latter three followed by the standard curing. Under the standard conditions, the flexural strength and compressive strength of Class C fly ash geopolymer mortars developed quickly until the age of 7 days, followed by a gradual increase. Specimens with Class F fly ash plus Ca(OH)2 showed slow increase till the age of 28 days. Under these non-standard conditions (2–4), all specimens showed higher 3-day strength, while later strengths were either higher or lower than those in standard conditions, depending on the type of the precursor.