100 / 2022-04-21 12:34:37

The mechanical properties, Drying shrinkage behavior and microscopic characteristics of sustainable concrete designed by seawater, sea sand, fly ash and limestone calcined clay under different curing ages

seawater and sea sand concrete; supplementary cementitious materials; micro characteristic; One year curing age; Compressive strength; Splitting tensile strength; drying shrinkage behavior

The shortage of fresh water and river sand resources and the high pollution discharge caused by mass production of cement are very serious, and the increasing depletion of fresh water and river sand leads to the destruction of river ecosystems, especially for coastal areas. Rich sea sand and sea water resources can alleviate this trend, so the study of sea sand concrete is an important way to achieve sustainable development. In order to systematically and comprehensively study the performance of seawater sand concrete and explore green environmental protection materials that can replace cement, the long-term mechanical, shrinkage and microscopic properties of 0.58, 0.48, 0.38 pure seawater sand concrete (SWSSC), 0.48 fresh water river sand control concrete and FA/LC2 seawater sand concrete with the dosage of 0%, 25% and 45% respectively were studied. After research, it is found that:

Adding sea water and sea sand will increase the early compressive strength of concrete and decrease its workability, but the strength of sea water and sea sand concrete after one year is not as good as that of the control fresh water and river sand concrete. With the increase of curing age, the comprehensive performance of SWSSC with FA/LC2 is close to or better than that of control SWSSC. There is a good correlation between curing age, water-binder ratio (FA/LC2 content), 4.5nm-50nm pores and drying shrinkage, and the 3-dimensional /2-dimensional relationship equation proposed by fitting can be used to predict the effect of SCM on drying shrinkage behavior of SWSSC. The pore analysis of SWSSC with different volumes of SCMs for one year shows that SCM is beneficial to increase the proportion of pores less than 50nm, and can effectively limit the drying shrinkage behavior of SWSSC. Scanning electron microscope (SEM) analysis shows that after long-term curing, the microstructure of SWSSC doped with SCMs is more uniform and compact, and the SWSSC with LC2 content of 25% has the best microstructure performance. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) also prove that LC2 system has better chemical reaction performance and higher early activity than FA system. It is worth mentioning that compared with adding FA, adding LC2 helps to make up for the early performance deterioration of SWSSC. However, compared with mixed LC2, FA can better optimize the matrix of SWSSC after one-year curing.