Phosphorus slag in supplementary cementitious and alkali activated materials: A review on activation methods

• Accelerated hydration of PS via activation methods is reviewed. • Review on using PS as blended cement in SCM and as a precursor in AAM. • Combined activation method has the best performance despite high PS as cement replacement. Supplementary cementitious materials (SCM) and alkali activated materials (AAM) are widely researched as alternative binder in concrete due to potential for reducing greenhouse gas emissions by utilizing industrial by-products. Phosphorus slag (PS) is the by-product of yellow phosphorus industry, which can partially substitute ordinary Portland cement (OPC) and reduce carbon footprint. This paper provides a comprehensive review of different activation methods (mechanical, thermal, chemical and alkali activation) to study the factors affecting the mechanical properties and underlying mechanism of PS as binder in SCM and precursor in AAM. The major drawback of PS in cement-based materials or concrete is the low early strength and long setting time due to the presence of P 2 O 5 , and this intensifies as the PS replacement amount increases. The mechanical activation by increasing the fineness, utilization of chemical activators and elevated curing temperature to improve the early-age performance of PS blended cement (PSC) are summarized. Specifically, the effect of these activation methods with different PS replacement level on cement paste, mortar or concrete are discussed in terms of compressive strength, setting time and microstructure. Combined activation gives the best outcome in improving early age properties of PSC. The composition of PS, replacement level and fineness of PS, curing temperature and method, type and dosage of activator are highlighted in this paper. Generally, the optimal PS replacement level is 30 – 40% in non-activated PSC, while activated PSC with proper activators can increase the PS replacement level to 35% – 80% or even fully replace OPC in AAM system.