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Waste plastics and rubber have always posed a threat to the environment and a great challenge for disposal. The use of these two waste materials as modifiers for road asphalt provides new road asphalt binders and at the same time provides a new way for waste material resource treatment. Rubber-modified asphalt and plastic-modified asphalt have received widespread attention due to their green and low-carbon characteristics and some performance advantages, but there are still some performance shortcomings that hinder their promotion and application. In order to continue to explore the application of waste materials in the field of road engineering, combined with the performance advantages of both, many scholars began to study the rubber-plastic composite modified asphalt (RPCMA). Therefore, this paper reviewed the different types of waste rubber and plastic, the comprehensive performance of different types of asphalt and its mixture performance, analyzed the modification mechanism of rubber-plastic composite modified asphalt and its performance changes. The results show that rubber-plastic composite modified asphalt is mostly prepared by directly adding modified materials. However, the pretreatment or melt granulation of rubber and plastic will make the performance of rubber-plastic modified asphalt has improved. There is a mutual promotion mechanism between rubber and plastic in asphalt, which makes the performance of rubber-plastic modified asphalt better than that of asphalt obtained by a single modification method (rubber modified asphalt or plastic modified asphalt). In some properties, it can be close to the commercial SBS modified asphalt. The performance of rubber and plastic composite modified asphalt at high temperature has been generally recognized by researchers, but its low-temperature performance is still controversial. Therefore, it is recommended to apply in high-temperature areas. Future work should focus on the development of composite modifiers with stable performance, low cost and ease of use, standardization of modification processes, improvement of low-temperature performance, and monitoring of road performance and environmental impact. [ABSTRACT FROM AUTHOR]

The accumulation of municipal solid waste incineration bottom ash (MSWI-BA) not only occupies land, but also leads to severe environmental pollution. In order to improve the utilization of MSWI-BA and reduce carbon emissions, the effect of alkali content on alkali-activated slag (AAS) paste containing 12% MSWI-BA under high-temperature exposure was studied. The alkali contents, i.e., the mass of Na2O in the water glass, were 2%–6% of the total mass of the precursors. The weight loss, thermal shrinkage, and strength of AAS were investigated. The results show that at the same heat treatment temperature, as the alkali content increases, the flexural and compressive strengths of AAS increase and then decrease, reaching the maximum at AAS with 4% alkali content (NS4). As the alkali content increases from 2% to 4%, the higher OH− concentration reduces the Ca dissolution of portlandite in MSWI-BA, resulting in a lower increase in Ca concentration than Si concentration. This leads to a decrease in Ca/Si and an increase in Al/Si of C─ A─ S─ H, which is beneficial for improving the structural stability of C─ S─ H after high temperature. When the alkaline content increases from 4% to 6%, excessive matrix shrinkage leads to an increase in microcracks. It was found that NS4 has the best high-temperature resistance and has good application prospects in engineering. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the combined influence of heat curing and partial replacement of silica fume on the long-term behavior of alkali-activated slag (AAS) mortar. Silica fume replacement levels of 0%, 5%, and 10% were examined, with curing conducted at temperatures of 23 ± 2 and 80°C. The alkaline activator consisted of sodium hydroxide solution (4 M) mixed with sodium silicate in a 3 : 1 ratio by weight. The performance of the fabricated specimens was evaluated through compressive strength testing, mass change analysis, X-ray diffraction, and scanning electron microscopy. Heat treatment resulted in improved performance of AAS mortars, while silica fume replacement also positively influenced mortar behavior. Notably, the 5% replacement rate yielded the most favorable outcomes. However, it was observed that the long-term compressive strength of AAS mortar specimens decreased significantly. Potential adverse factors contributing to this decline were discussed. Furthermore, the durability of mortar samples exposed to adverse conditions was investigated. Results indicated that the combined use of heat curing and a 5% silica fume replacement level produced the best overall performance. [ABSTRACT FROM AUTHOR]

In this paper, effects of curing methods (i.e. curing at ambient temperature (A), in oven (O) and in boiling water (BW)), NaOH solution concentration (i.e. 8 and 12 moles/liter) and disc thickness (i.e. 1, 2 and 3 cm) on pull-off strength (POS) of the geopolymer concrete containing Ground Granulated Blast Furnace Slag (GGBFS) and Natural Zeolite Powder (NZP) have been investigated. The results show that the value of the POS obtained from the 3 cm thickness disc is on average 2.6% higher than that obtained from the 2 cm thickness disc. This implies that the discs with thicknesses of 2 and 3 cm have given approximately equal values of the POSs. Moreover, the value of the POS obtained from the 2 cm thickness disc is on average 28.4% higher than that obtained from the 1 cm thickness one. Based on the results obtained from the 2 cm thickness disc: a) the ratios of the POSs of the samples cured in boiling water and oven to that of the specimen cured at ambient temperature have been obtained on average equal to 1.383 and 1.089, respectively. b) as 20% wt. of the GGBFS is substituted by the NZP, the value of the POS reduces by an average of 16.29%. c) as the NaOH solution concentration increases from 8 to 12 mole/liter, the value of the POS increases by an average of 14.48%. From the results, there is a strong nonlinear relationship between the compressive and pull-off strengths of the geopolymer concrete. [ABSTRACT FROM AUTHOR]