The requirements for modified asphalt concrete are increasing because of heavy traffic load and worsening service environments in modern highway construction. More and more attention has been paid to the development of multifunctional asphalt concrete. Conductive asphalt concrete exhibits specific characteristics and incredible novel features, such as self-diagnosis and monitoring, self-healing, and snowmelt, etc. It has the potential to satisfy multifunctional applications. This article summarizes the major achievements of the existing literatures about conductive asphalt concrete, including material design, mechanism analysis, performance evaluation and engineering applications, and gives some proposals for further investigations. The article shows that the conductivity and mechanical properties of conductive asphalt concrete are strongly dependent on the compositions of the material. Meanwhile, the mechanism of conductivity improvement is identified according to the characteristics of conductive additives. Although conductive asphalt concrete has some shortcomings and few applications in the highway industry, it shows some appreciable advantages in aspects such as environment protection and traffic safety. The purpose of this review article is to provide the reference and guidance for researchers to discover proper material design, novel properties, durability, and desirable high operational efficiency, as well as suitable construction technique.

Sodium sulfate (Na₂SO₄) and sodium carbonate (Na₂CO₃) are weakly alkaline activators. Alkali-activated slag (AAS) cement prepared with them shows the special advantages of long setting time and low shrinkage, but it shows slow development of mechanical properties. In the paper, Na₂SO₄ and Na₂CO₃ were used as activators and compounded with reactive magnesium oxide (MgO) and calcium hydroxide (Ca(OH)₂) to optimize the setting time and mechanical properties. The hydration products and microscopic morphology were also studied using XRD, SEM, and EDS. Furthermore, the production cost and environmental benefits were compared and analyzed. The results show that Ca(OH)₂ is the main influencing factor for setting time. It reacts preferentially with Na₂CO₃ to form CaCO₃, which makes AAS paste lose plasticity rapidly and shortens the setting time, and then produces strength. Na₂SO₄ and Na₂CO₃ are the main influencing factors for flexural and compressive strength, respectively. Suitably high content is beneficial to promote the development of mechanical strength. The interaction of Na₂CO₃ and Ca(OH)₂ shows a great effect on the initial setting time. High content of reactive MgO can shorten the setting time and increase the mechanical strength at 28 days. There are more crystal phases in hydration products. Considering the setting time and mechanical properties, the composition of activators are: 7% Na₂SO₄, 4% Na₂CO₃, 3–5% Ca(OH)₂, and 2–4% reactive MgO. Compared with ordinary Portland cement (OPC) and AAS cement activated by sodium hydroxide (NaOH, NH) and water glass (WG) with the same alkali equivalent, the production cost and energy consumption are greatly reduced. Compared with P·O 42.5 of OPC, CO₂ emission is reduced by 78.1%. AAS cement activated by weakly alkaline activators shows excellent environmental and economic benefits and good mechanical properties.

Brick waste makes up a significant part of the solid waste that is generated from building demolition globally. The disposal of this waste consumes land, causes environmental pollution, and is a waste of resources. In order to use this construction waste and increase its functionality, two types of stable-shape PEG-400/SiO₂ composite shaped PCM and Tet/SiO₂ composite shaped PCM were studied and added to recycled aggregate pavement bricks, and two new types of composite shaped PCM recycled aggregate pavement bricks were created. SEM, DSC, TGA, and other test methods found the two PCMs to be successfully adsorbed by SiO₂, and the setting effect of PEG-400/SiO₂ was found to be better than that of Tet/SiO₂. The physicochemical properties of both composite shaped PCMs remained stable within the TGA test temperature range. The prepared PCM was added to the recycled aggregate pavement brick. A comprehensive analysis of the properties of the composite shaped PCM recycled orthopedic pavement brick found the compressive strength and flexural strength of Tet/SiO₂ PCM recycled aggregate pavement brick to be significantly higher than those of PEG-400/SiO₂ PCM recycled aggregate pavement brick. With a recycled aggregate content of 60% and a compound shaped PCM content of 5%, the 28-day strength of the recycled aggregate pavement brick was found to be higher than that of the recycled aggregate pavement brick with a recycled aggregate content of 70% and a compound shaped PCM content of 10%. This study provides reference for the optimization and upgrading of the thermal storage performance of composite shaped PCM in practical applications, and is of great significance for promoting thermal energy storage development and expanding its application range.

As a relatively fast-setting building material, desulfurized gypsum is difficult to use. Citric acid, sodium gluconate, and sodium tripolyphosphate were used to design and prepare a desulfurized gypsum paste containing single or combined retarders. The effects of the retarder type and content on the setting inhibition and mechanical properties of desulfurized gypsum were evaluated. The experimental results showed that all three retarders had different degrees of retardation on desulfurized gypsum; among them, citric acid had the best retarding effect. When the citric acid content was 0.10 %, the initial and final setting times were 25 and 31 min, respectively. However, the mechanical properties of desulfurized gypsum could be decreased by more than 60 %. Compared with single-doped retarders, combined retarders had obvious advantages. They not only significantly lengthened the setting time and hardening time two-fold or even more but also the compressive strength of desulfurized gypsum with combined retarder was 50 % higher than that with single retarder under the same retarding effect as a single retarder. The hydration heat curve provided insight into the setting inhibition of desulfurized gypsum by retarders. Scanning electron microscopy images showed the change in the crystal morphology of desulfurized gypsum-hydrated crystals with the addition of retarders. The addition of a retarder lengthened the induction period of desulfurized gypsum and changed the morphology of desulfurized gypsum-hydrated crystal, thus extending the setting time and reducing the strength.