Assessment of Feasibility of Sintered Fly Ash Lightweight Aggregate as an Effective Self-Curing Additive for Sustainable Concreting Practice

AIKTC, SoET, Civil Engineering Department, Panvel, Navi Mumbai, India

^* Corresponding author: dada.patil@aiktc.ac.in

Abstract

Effective curing is an essential requirement for a desired long-term performance of concrete. For 1 cubic metre of hardened concrete, 3 cubic metre of water is required; most of which is consumed for curing, thereby leading to an unsustainable practice. Limited depth of water penetration occurs in conventional method of external curing. Self-Curing (SCu), also known as Internal Curing facilitates uniform moisture distribution throughout the concrete. Moreover, enormous amount of curing water can be saved for a sustainable development. This is achieved by incorporating prewetted porous lightweight aggregates (LWAs); water held in LWA pores is gradually desorbed in to surrounding matrix over a period of time for an effective Self-Curing by maintaining sufficient moisture inside the concrete mass. Different types of LWAs are used for this purpose. The available literature indicates that sintered fly ash LWAs are used to produce non-structural and structural lightweight concrete; but their utilization for internal curing is not found. In this experimental work, feasibility of 4 to 8 mm spherical sintered fly ash LWA to act as an effective Self-Curing agent was assessed through various tests. Scanning Electron Microscopy revealed that LWAs were porous enough to hold sufficient amount of water. Higher specific gravity as compared to that of other types of LWAs made it desirable material from strength and density point of view. Higher water absorption rate within initial 30 minutes reflected it’s better desorption behaviour; highly desirable for an effective internal curing. Oven-dried LWAs were immersed in blue ink for 24 hours and then placed in a white cement paste. The thick blue ink corona around LWA confirmed about better desorption. This is not true of every type of LWA. Cement-sand mortar cubes were cast by volumetrically replacing sand by 10%, 15% and 20% prewetted LWAs for compressive strength tests at 3, 7 and 28 days. Prewetting was done for 24 hours and 72 hours. Conventional mortar cubes were placed under water; prewetted LWA-incorporated specimens were placed inside laboratory in an open air and directly under the sun. Conventional specimens exhibited highest strength values. Among Self-Curing specimens, 15% LWA cubes indicated maximum compressive strength; marginally less than that of water- cured cubes. 72-hour prewetted LWA cubes resulted in higher strengths as compared to that of 24 hour prewetted LWA cubes. Ultrasonic Pulse Velocity values for all the specimens were between 3.16 to 3.68 km/sec. The experimental results indicated that sintered fly ash LWA can be used as a potential material to produce Self-Curing concrete.