Influence of Activator Na2O Concentration on Residual Strengths of Alkali-Activated Slag Mortar upon Exposure to Elevated Temperatures

Abstract

The mechanical strength variation of ambient cured Alkali-activated mortar (AAS) upon exposure to elevated temperatures from 200 to 1200 °C was studied in this article. Slag was activated by the combination of sodium silicate liquid (Na2SiO3) and sodium hydroxide (NaOH) with different Na2O concentrations of 4%, 6%, 8%, and 10% by slag weight. Mechanical properties comprising compressive strength, flexural strength, and tensile strength before and after exposure were measured. Thermogravimetric analysis (Thermogravimetric analysis (TGA) and Derivative thermogravimetric (DTG)), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS) were also used for strength alteration explanation. The results indicated that Na2O concentration influence on strength variation of AAS mortar was observed clearly at temperature range from ambient temperature to 200 °C. The melting alteration of AAS mortar after exposed to 1200 °C was highly dependent on concentrations of Na2O.

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

“…The further micro-crack formation from shrinkage may have caused the flexural strength loss of the AAS mortars at elevated temperatures. When subjected to a high temperature of 200 °C, the mortar experienced drying shrinkage due to water evaporation, and chemical shrinkage resulted from further reactions [40]. The formation of cracks due to this mechanism did not occur in the A specimens.…”

A Review of Durability and Strength Characteristics of Alkali-Activated Slag Concrete

“…The typical range of Na 2 O examined is 4–10% by weight of GGBS. Up to curing temperature as high as 800 °C, increase in Na 2 O from 4% to 6% is accompanied by significant increase in compressive strength [37]. However, unlike curing at elevated temperature, Guerrieri and Sanjayan [38] reported that oven drying of AAS paste at only 40–50 °C leads to total disintegration and loss of strength of the samples.…”

“…Tran and Kwon [37] studied the effect of sodium oxide concentration (Na 2 O) of the alkaline activator solution on residual compressive strength of 40 mm × 40 mm ×160 mm AAS mortar samples. Figure 4 shows that compressive strength loss begins or continues at 200 °C but significant loss of compressive strength occurs when mortar AAS samples are subjected to more than 600 °C, regardless of the content of Na 2 O.…”

“…Effect of elevated temperature and sodium oxide concentration on residual compressive strength [37]. …”

Influence of SiO2, Al2O3, CaO, and Na2O on the elevated temperature performance of alkali‐activated treated palm oil fuel ash‐based mortar

“…The previous research works have revealed that the reactivity and reaction mechanism of blended SMs‐based AAB were affected by the increase in the curing temperature and/or Na 2 O concentration of the AA 21,22 . There are limited numbers of reports on the effect of Na 2 O concentrations on the thermal stability of AAB after being exposed to various elevated temperatures 23–25 . The effect of various Na 2 O concentrations (4, 6, 8, and 10%) relative to the weight of AAB, on the alkali‐activated slag (AAS) mortar products after exposure to various elevated temperatures has been previously studied 25 .…”