Safety and environmental protection application of high performance solid waste unburned ceramsite and its lightweight high strength concrete

The utilization of solid waste building materials is conducive to the green and low-carbon development of the construction industry. In this study, fly ash, red mud and other solid waste were used to prepare high-performance solid waste unburned ceramsite, and the mix ratio design of lightweight high-strength concrete was carried out. The main conclusions are as follows: The prepared solid waste unburned ceramsite has a compressive strength of 8.9 MPa, a bulk density of 556 kg/m3, and a 1 h water absorption of 5.9%, which meets the relevant requirements of "Lightweight aggregates and its test methods-Part 1: Lightweight aggregates" (GB/T 17431.1–2010). Microstructure analysis demonstrated that the internal hydration products of unburned ceramsite were mainly hydrated calcium silicate and ettringite. On the basis of the detection and analysis of the content of six heavy metals in unburned ceramsite, the pollution assessment results of unburned ceramsite were consistent by means of the environmental assessment. That is, there is no environmental risk for the six heavy metals. At the same time, the Cr, As and Cd in unburned ceramsite need to be controlled, as they pose a carcinogenic risk to the human body. Therefore, the risk control of heavy metals Cr, As and Cd in unburned ceramsite was carried out. The 28 d compressive strength of lightweight high-strength concrete (cement 756 kg, silica fume 42 kg, slag powder 42 kg, floating beads 210 kg, ceramsite 165 kg, water reducer 16.8 kg, defoamer 2 kg, thickener 5 kg, water 218.4 kg) prepared by unburned ceramsite can reach 45.2 MPa, the dry apparent density is 1435 kg/m3, and the slump and expansion are 240 mm and 635 mm respectively, which meet the relevant requirements in the "Technical standard for application of lightweight aggregate concrete" (JGJ/T 12–2019). By calculating the carbon emission reduction of unburned ceramsite lightweight high-strength concrete, it is found that the carbon emission generated during the production and transportation of unburned ceramsite lightweight high-strength concrete is much smaller than that of ordinary lightweight high-strength concrete. The above results can provide basic theoretical support for the utilization of solid waste resources for lightweight high-strength concrete.