Author: Kamal H. Khayat

Publisher:

Published: 2018

Total Pages: 82

ISBN-13:

The project presented in this report aimed to develop an effective methodology to use saturated lightweight sand (LWS) for internal curing to enhance concrete performance and prolong service life of concrete structures. High-performance concrete (HPC) mixtures approved by MoDOT for pavement and bridge deck structures were used for the baseline mixtures. Five different types of saturated LWS employed at various contents were investigated to evaluate the optimum dosage of LWS and maximize its effectiveness on enhancing concrete performance. The content of LWS was varied to ensure the introduction of internal curing water that can secure up to 150% of the water consumed by chemical shrinkage during cement hydration (As per ASTM C1761). Performance improvement from the LWS focused mainly on reducing autogenous and drying shrinkage and the resulting cracking potential without sacrificing durability and cost competence. Proper combinations of internal and external curing were found to enhance shrinkage mitigation. Under 7 days of initial moisture curing, HPC made with the LWS3 resulted in the lowest overall shrinkage. The Bridge-LWS2-150% exhibited the best performance in mitigating autogenous shrinkage where the concrete maintained 160 micro-strain of expansion even after 175 days of age. The lowest drying shrinkage was obtained with the Bridge-LWS3-50% mixture (340 micro-strain) at 175 days subjected to 28 days of moist curing. For the paving HPC, the lowest drying shrinkage at 155 days was obtained with the Paving-LWS3-150% mixture (265 micro-strain) subjected to 28 days of moist curing. Concrete proportioned with the LWS2 expanded shale LWS exhibited the best compressive strength, regardless of the curing regime. In terms of initial moisture curing duration, the application of 7 days of moisture curing resulted in the highest compressive strength compared with other curing conditions. The 56-day compressive strength of HPC designated for bridge deck construction that was made with the LWS1 was up to 10 MPa (1,450 psi) greater than the Bridge-Reference concrete made without any LWS. The Bridge-LWS2-100% and Bridge-LWS1-50% mixtures exhibited the highest 56-day MOE of 42.5 GPa (6,615 ksi) under Standard curing. The Bridge-LWS3-100% mixture cured under Standard conditions had the highest 56-day flexural strength of 5.5 MPa (800 psi). The mixtures made with LWS2 presented the lowest sorptivity, regardless of the curing condition and LWS content. The findings from this comprehensive project provided a basis for: (1) new mixture design methodology and guidelines for using LWS for internal curing for bridge deck and pavement applications; and (2) validation of performance improvement when using internal curing and cost competitiveness in the State of Missouri.