Mechanical and durability properties of sea-water sea sand concrete

Abstract

With the increase of infrastructure construction worldwide, the supply of river sand and fresh water for making concrete faces huge shortage, especially in coastal areas where major urban centers are located. To alleviate this problem, the making of concrete with seawater and sea sand (together with fiber reinforced polymer reinforcements that will not corrode) has received attention from the civil engineering community. This thesis focuses on several mechanical and durability properties of seawater sea sand concrete that are important for practical applications. The mechanical and microstructural properties of seawater sea sand concrete are first investigated. Three types of concrete: ordinary concrete (OC), sea sand concrete with fresh water (SC) and seawater sea sand concrete (SSC) were prepared with two different water/binder ratios. Compressive strength, flexural strength, dynamic modulus of elasticity, and stress-strain relationship were measured and microstructural analysis of all the concrete types were carried out. The results showed that the early age compressive strength increased due to the use of seawater and sea sand but slightly decreased at 28 days. Compared with ordinary concrete, the flexural strength SC and SSC were higher at both 7 and 28 days. The dynamic modulus of elasticity of concrete was also increased when seawater or seawater and sea sand were used, especially at the early age. Scanning electron microscopy (SEM) analyses were conducted to provide support to these results. Then the influence of carbonation on the mechanical properties of the three types of concrete described above is studied. The results showed that the compressive strength for all three types of concrete increased with the extension of carbonation time. The net increase of compressive strength (excluding effect of cement hydration) contributed by carbonation of SSC and SC was less than OC. For the three types of concrete, the ascending branches of the stress-strain curves curves were similar. For the descending branches, the slop of SSC and SC became steeper compared with OC after carbonation. The results indicated that the brittleness of SSC and SC increased with carbonation time. Durability of concrete is affected by the penetration of water and dissolved chemicals. The capillary water absorption test was therefore carried out. The test results showed the highest cumulative water absorption in OC, followed by SC and SSC. Shrinkage of concrete is of relevance to practical applications. Results of free shrinkage test showed that the shrinkage strain of OC was the largest, followed by those of SC and SSC under the same curing age. Based on the GL2000 model, a new prediction model for the shrinkage of SSC and SC was established by introducing an expansion effect coefficient. The proposed model could accurately predict the development of the shrinkage strain in OC, SC, and SSC.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Christopher Kin Ying LEUNG (Supervisor)