Mechanical properties and ultrasonic velocity of lightweight aggregate concrete containing mineral powder materials

There is a global material recycling trend to save energy and reduce carbon. This study used four renewable slag admixtures, including fly ash, blast furnace slag (GGBFS), desulfurization slag, and glass powder, to replace some of the cement in lightweight aggregate concrete (LWAC). Then, its mechanical properties and ultrasonic pulse velocity were investigated. A fixed water/binder ratio (0.40) was used to make the LWAC, with the four renewable slag admixtures (fly ash, GGBFS, desulfurization slag, and glass powder) replacing 0, 10%, or 30% of the cement. Then, the properties of the fresh concrete were tested, along with those of the hardened concrete and the ultrasonic pulse velocity at various ages. The results indicated that when the addition of renewable slag admixture was 10%, the compressive strength increased with age. Moreover, the late compressive strength obviously increased when the addition of GGBFS or fly ash was 30%. At the age of 28–120 days, the fly ash group had the highest compressive strength among the mixtures with 30% renewable slag admixture, followed by the GGBFS group, glass powder group, and desulfurization slag group. The correlation coefficient (R²) values for the concrete elastic modulus and compressive strength values of the control, fly ash, GGBFS, desulfurization slag, and glass powder groups were 0.9537, 0.7888, 0.9742, 0.9665, and 0.9161, respectively. In addition to the fly ash group, various mixes showed favorable correlations between these two items. The mixes with the 30% addition showed larger fluctuations in the ultrasonic pulse velocity, with the increase in the ultrasonic pulse velocity varying with the kind of renewable slag admixture. A regression analysis of the ultrasonic pulse velocity and compressive strength of each mix proportion showed that the correlation coefficients of the control, fly ash, and GGBFS groups were larger than 0.88, whereas the correlations for the desulfurization slag and glass powder were relatively low, with R² values of only 0.5577 and 0.7415, respectively. The 30% desulfurization slag group had the highest expansion response among the mixes. The mix with the 30% renewable slag admixture had a higher expansion response than the 10% mix. The findings demonstrated that a quantity of mineral powder material had positive benefits for the mechanical properties and ultrasonic pulse velocity of the LWAC, as well as providing energy saving and carbon reduction advantages.