138 / 2022-04-29 00:26:23

Study on the durability of seawater and sea-sand concrete

Seawater and sea sand concrete; Fly ash; Limestone calcined clay; Mechanical strength; Drying shrinkage behavior

Adopting greener and lower carbon materials in cement industry, such as limestone calcined clay (LC2), fly ash (FA) and slag as supplementary materials, is the key breakthrough of energy saving and emission reduction. Additionally, a large amount of concrete in the construction industry every year leads to the consumption of fresh water and river sand increasing. The shortage of fresh water and river sand may lead to the destruction of river ecosystem, especially for coastal regions. Therefore, it is an important approach to study the replacement of fresh water and river sand by seawater and sea sand to improve resources shortage and achieve sustainable development. Based on the concept of global resource depletion and sustainable development, seawater and/or sea sand (mainly seawater) have interesting application values in the fields of unreinforced concrete, FRP reinforced concrete, ICCP-SS (Impressed Current Cathodic Protection-Structural Strengthening) and so on. In this study, eight kinds of concrete were designed by using three different water-binder ratios, two supplementary cementitious materials (SCMs). This study reports the comprehensive results of workability, mechanical strength, drying shrinkage behavior and microstructures of seawater and sea sand concrete (SSC). At the same time, to fully analyze mechanical properties and deformation properties, SSC hydration products and the characteristics of the SSC microstructures is explored by XRD, TGA, SEM-EDS and MIP.



The results show that adding seawater and sea sand can lead to the increase of early compressive strength and the declining of concrete workability, while the utilization of seawater and sea sand can result in the decrease of later strength (Fig. 1). With the rising of curing age, SSC with adding SCMs (FA/LC2) has similar or better comprehensive performance than OPC-SSC. The MIP results (Fig. 2) show that the pore structure of SSC can be refined by using seawater and sea sand, reducing water-binder ratio and replacing OPC with FA/LC2. The pore structure of SSC is closely related to its drying shrinkage behavior (Fig. 3). Scanning electron microscope (SEM) analysis (Fig. 4) also confirmed that the SSC with mineral admixtures has a more uniform and compact microstructure after long-term curing, and the SSC with 25% LC2 content has the best microstructural property. X-ray diffraction (XRD) and thermogravimetry analysis (TGA) also proved that LC2 system had better reaction performance and higher early activity than FA system (Figs. 5 and 6). This study can provide an insight into the utilization of seawater and sea sand in concrete and the impact of SCMs on SSC.