Investigation of workability and durability of concrete mixes incorporated with expansive cement, poly-carboxylate admixtures, and lightweight aggregates

Abstract

Calcium Sulfoaluminate (CSA) cement is renowned for rapid strength development, accelerated microstructure formation, and shrinkage mitigation. It has been used as a supplemental cementitious material for concrete decks of bridges, airport runways, and several other practical applications. One of the main disadvantages of using CSA cement is its high-water demand for rapid hydration processes, which adversely affects the fresh concrete workability. In this study, different poly-carboxylate admixtures have been used to prepare several concrete mix test batches. These concrete mixes include Ordinary Portland cement (OPC) and Type K (85% OPC + 15% CSA) cement mixes. Slump and air content readings were taken within 60 minutes from the time of mixing. A specific mid-range water-reducing admixture (MRWRA) effectively retained the flowable properties at the end of 60 minutes, acceptable for working conditions. Isothermal calorimetric studies were performed after preparing different cement pastes samples with added admixtures; MRWRA keeps the Type K cement paste at the dormant stage for the longest time effectively compared to other admixtures. However, this raises questions about the quality of microstructure development during the curing process. Further tests were done, adhering to the ASTM standards, incorporating the pre-soaked lightweight aggregates (LWA) and MRWRA in the concrete mix designs. Several samples were prepared for the water absorption test and compressive strength test. Data trends concluded that KL35MR (Type K samples with MRWRA at 3 fl oz/cwt and 35% replacement of fine aggregates with LWA) had demonstrated the lowest permeability after 7 days submerged underwater. Also, these samples had the highest compressive strength amongst all Type K samples. These observations were relatable to normal OPC concrete samples and can thus, KL35MR concrete mix design can be considered durable for bridge decks and other structural applications. For further justification, further analysis should be done at a micro-level, such as scanning electron microscopic imaging, to understand the impact of internal curing and retarding admixture interaction on microstructure development of expansive cementitious materials.