Utilization of coal-based synthetic natural gas slag as road base construction material through geopolymerization

Abstract

The development of the Coal-based synthetic natural gas industry inevitably produced lots of slags. The application of coal-based synthetic natural gas slag (CSNGS) to road base not only effectively alleviated the accumulation and pollution of CSNGS, but also reduced the consumption of resources, which had significant economic and social benefits. However, CSNGS has a higher crushing value and water absorption, thus its mix design, mechanical properties and pavement performance must be further investigated when applied as the raw material of novel cementing material and aggregate. The purpose of this study is to investigate and comparatively analyze the optimal mixing ratio and mechanism of the strength of CSNGS applied in road base. For this, this study prepared the precursor of geopolymer by milling CSNGS into powder and mixing it with 20% cement. Then sodium hydroxide and sodium silicate were used as alkali activators to activate CSNGS, and the 7d unconfined compressive strength was used as the evaluation index to develop the optimal mix ratio of coal-based synthetic natural gas slag geopolymer (CSG). CSNGS with particle sizes ranging from 0 to 4.75 mm and 0 to 9.5 mm were used as aggregates to replace natural stones, then the cement and CSG were selected respectively to stabilize the slags-aggregates, and the relevant tests were carried out to investigate the mechanical and road properties. The results showed that the performance of CSG stabilized aggregates was lower than cement stabilized aggregates in the tests of unconfined compressive strength, splitting strength, unconfined compressive modulus of resilience, dry-wet cycles, and freeze–thaw cycles. The performance of the mixture deteriorated with the incorporation of CSNGS when the cementitious material was cement. The temperature shrinkage test found that the shrinkage of CSG stabilized specimens was less than cement stabilized specimens, which indicated that CSG had excellent anti-cracking potential. In addition, the temperature shrinkage coefficients of mixtures with different CSNGS dosages varied with temperature when the cementitious material was cement. Finally, to further verify the macroscopic test results, this study combined with scanning electron microscope (SEM) test to deeply analyze the strength formation mechanism of several mixtures.