Effects of sodium aluminate on the performance of seawater sea-sand engineered cementitious composites

In this study, a quick setting seawater sea-sand engineered cementitious composite (SS-ECC) was prepared using sodium aluminate (NaAlO2, NA). The effects of the amount of NA and different types of water (seawater and freshwater) on the setting time, compressive strength, flexural strength, and tensile properties of the SS-ECC were studied. The influence of NA on the hydration reaction and microstructure of the SS-ECC was examined through X-ray diffraction (XRD), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FE -SEM). Experimental results revealed that NA and seawater reduced the setting time of the SS-ECC, particularly at 4% NA, and slightly improved the early strength of the SS-ECC. However, too much NA would decrease the late strength of the SS-ECC. The incorporation of NA enhanced the ultimate tensile strain of the SS-ECC. And the SS-ECC with 4% NA exhibited evident strain-hardening characteristics under tension, with the ultimate tensile strain reaching a maximum of 4.61%. The calculated toughness and residual strength indexes indicated that the SS-ECC could be defined as an ideal elastoplastic material. Based on this, a bilinear uniaxial tensile stress-strain constitutive model of the SS-ECC was established. In addition, the XRD and TGA results demonstrated that NA promoted the hydration of cement, generation of AFt and AFm, and polycondensation reaction to generate C-A-S -N and N-A-S-H gels. This decreased the setting time of the SS-ECC and improved the early strength. However, the product obtained by the early rapid reaction might have encapsulated the cement raw materials, thereby pre-venting further hydration in the later stage. This was not conducive to the long-term strength development of the SS-ECC.

Automated summary

In this study, a quick setting seawater sea-sand engineered cementitious composite (SS-ECC) was prepared using sodium aluminate (NaAlO2, NA). The effects of the amount of NA and different types of water (seawater and freshwater) on the setting time, compressive strength, flexural strength, and tensile properties of the SS-ECC were studied. The incorporation of NA reduced the setting time and slightly improved the early strength of the SS-ECC, but too much NA decreased the late strength. The inclusion of NA enhanced the ultimate tensile strain of the SS-ECC, making it an ideal elastoplastic material.