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Nowadays, significant research effort is being dedicated to explore environmentally friendly block materials with high strength and high-temperature resistance. Ground-granulated blast-furnace slag (GGBFS) is produced during the iron smelting waste process and can be activated to form the environment friendly alkali-activated slag cementitious material (AASCM) when mixed with alkaline activator. The aggregate consists of particles of different sizes, which are crushed and are screened using the paste of AASCM. In this study, the compressive strengths of 234 block specimens during and after high-temperature treatment were investigated. The test results showed that the compressive strength of the blocks gradually decreased slowly when the temperature was lower than 600°C, and decreased rapidly when the temperature was above 600°C. The reduction coefficient of compressive strength of the blocks during and after 900°C exposure were 14.2% ~ 28.1% and 15.3% ~ 28.7% of the ambient temperature strength, respectively. The steel fibre reduced the compressive strength loss of the blocks during and after the high-temperature exposure. With the increase of temperature, the steel fibre lost its effect gradually. Moreover, the compressive strength of the block after the high-temperature treatment was higher than that during the treatment when the strength level and temperature remained constant, the ratio was between 0.99 and 1.14. The high-temperature strength loss of the alkali-activated slag crushed aggregate concrete block was lower than that of the alkali-activated slag ceramsite concrete block. The fitted equations for calculating the compressive strength during and after the high-temperature treatment provided a basis for evaluating the fire resistance of this new type of block. The microstructure and composition of the block were analysed through scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results provide theoretical basis and data support for the application of AASCM in masonry blocks in high-temperature environments. [ABSTRACT FROM AUTHOR]

The use of blast furnace slag improves resource utilization and supports the achievement of sustainable development goals. The use of alkali-activated slag cementitious material (AASCM) provides a new direction for improving the fire resistance of masonry structures. The masonry investigated in this study was alkali-activated slag crushed aggregate concrete masonry (ASCCM) in which aggregates of blocks and mortars were crushed and screened using AASCM paste specimens. The compression behavior of 12 specimens during and after exposure to high temperatures, specifically 300, 500, 600, 700, 800, and 900°C was investigated. The specimens were maintained under the target temperature for 2 h. The compressive strength and axial deformation of the specimen were recorded. The compressive strength losses during exposure to 300, 500, 600, 700, 800, and 900°C are 15.9, 20.3, 38.3, 43.9, 63.3 and 73.8%, respectively. The compressive strength losses after exposure to 300, 500, 600, 700, 800, and 900°C are 10.6, 15.8, 34.0, 37.2, 58.6 and 72.2%, respectively. The rate of loss in elastic modulus is greater than that in compressive strength. During exposure to 300, 500, 600, 700, 800, and 900°C, the loss rates of elastic modulus are 56.5, 74.4, 83.3, 86.3, 92.9 and 93.9%, respectively. After exposure to 300, 500, 600, 700, 800, and 900°C, the loss rates of elastic modulus are 49.6, 67.3, 77.5, 82.0, 90.7 and 94.5%, respectively. The peak compressive strain values are 9.9 and 11.1 times that at room temperature. Equations for calculating the compressive strength, elastic modulus, peak compressive strain, and ascending section curve of the stress–strain relationship with temperature were derived. The research results provide a new choice for high temperature resistant masonry materials, and provide theoretical basis and data support for the application of AASCM in masonry structures in high-temperature environments. [ABSTRACT FROM AUTHOR]

• Bond properties of alkali-activated slag concrete hollow block masonry are studied. • Shear strength, flexural strength and axis tensile strength of masonry were tested. • The effect of mortar strength grade on bond properties of masonry was evaluated. • Higher mortar strength lead to higher bond strengths of masonry. • Practical equations were developed to estimate mechanical properties of masonry. 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. [ABSTRACT FROM AUTHOR]

Highlights • A mixture of Na 2 CO 3 and NaOH was used as alkaline activator for AAS mortars. • Properties and microstructural characteristics of AAS mortars were investigated. • Characteristics of AAS mortar depend on Na 2 CO 3 -to-NaOH ratios and Na 2 O contents. • Na 2 CO 3 can prolong the setting time and improve compressive strength of AAS mortar. • Both Na 2 CO 3 -to-NaOH ratio and Na 2 O content obviously affected drying shrinkage. Abstract 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/Na 2 CO 3 solutions) on the performance of alkali-activated slag (AAS) mortars with pottery sand as fine aggregate. Five Na 2 CO 3 -to-NaOH ratios of 0/100, 20/80, 40/60, 60/40, and 80/20, and three Na 2 O 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 Na 2 CO 3 -to-NaOH ratio and Na 2 O content had a significant effect on the fresh and hardened properties of AAS mortars. A high Na 2 CO 3 -to-NaOH ratio and low Na 2 O content resulted in AAS mortars with longer initial and final setting times. The higher Na 2 CO 3 -to-NaOH ratios led to a higher late compressive strength of AAS mortars, where the 6% Na 2 O samples showed the best performance with Na 2 O contents of 4–8%. In addition, the drying shrinkage behavior of AAS mortars as a function of Na 2 CO 3 -to-NaOH ratio was dependent on the Na 2 O content. Moreover, the compressive strength and drying shrinkage have a direct relationship with the microstructure of AAS mortars. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study investigated the properties of alkali-activated slag (AAS) pastes with NaOH and a blend of NaOH and Na 2 CO 3 as the alkaline activator. The effects of five different Na 2 CO 3 to NaOH molar ratios (0:10, 0.9:10, 2.5:10, 5.7:10 and 15:10) and three different Na 2 O 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 Na 2 CO 3 to NaOH molar ratios and Na 2 O contents are major factors influencing the fresh and hardened pastes. Higher Na 2 CO 3 to NaOH molar ratios yielded a longer setting time and higher compressive strength. The Na 2 O content of 6% was more sensitive to the properties compared with 4% and 8% Na 2 O. When the Na 2 O content was 4%, the drying shrinkage increased as the Na 2 CO 3 to NaOH molar ratio increased; however, when the Na 2 O content increased to 6% and 8%, the drying shrinkage decreased as the Na 2 CO 3 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 Na 2 CO 3 to NaOH molar ratio of 15:10 and Na 2 O content of 6% can be regarded as the optimum mix proportion. [ABSTRACT FROM AUTHOR]