287 / 2023-01-21 14:45:56

The Mechanism of Performance Difference Between Seawater Sea-sand and Freshwater River-sand Ultra High Performance Concrete Based on X-CT Technology

sea sand,UHPC,X-CT,pore structure,steel fibre structure,mechanism analysis

At present, river sand was the main source of sand for construction. But the supply of river sand was limited by resources and environmental impact, and cannot fully met the demand for construction. China's coastal areas were rich in sea sand resources, and the total amount of sea sand resources in China's offshore was about 67.96×10¹⁰ ~ 68.49×10¹⁰ m³. The mining of sand for construction has gradually shifted to the marine environment. The orderly development, research and utilization of abundant sea sand resources as construction aggregates has become an inevitable development trend. How to use sea sand to prepare innovative water conservancy construction materials with excellent mechanical and durable properties is an intense and urgent task.

Based on the preparation principle of UHPC, sea sand and artificial sea water were used to replace river sand and fresh water to prepare seawater sea-sand ultra high performance concrete (SSUHPC), and freshwater river-sand ultra high performance concrete (FRUHPC) was prepared for comparative study. The compressive strength of SSUHPC and FRUHPC is 162.1 MPa and 173.3 MPa, respectively. Both SSUHPC and FRUHPC have high fatigue resistance characteristics, and SSUHPC takes the lead in stress failure in high stress fatigue test. Both SSUHPC and FRUHPC show excellent durability characteristics, while SSUHPC performs better. The microstructure characteristics of SSUHPC and FRUHPC were studied by SEM, XRD and MIP technology. The continuous section data were obtained by μX-CT technology, and the fibre and pore structure were reconstructed and established, so as to study the performance difference mechanism between SSUHPC and FRUHPC.

Hydration degree of mortar, characteristics of pore structure and dispersion of steel fibre were important factors on mechanical properties and durability of concrete materials. Excellent mechanics and durability of UHPC were guaranteed by uniformly dispersed steel fibre, hydrated cement mortar with mature structure and reasonable pore structure. Compared with FRUHPC, the mortar in SSUHPC has a higher degree of hydration, and the mortar with mature hydration structure and dense structure make the concrete material have higher corrosion resistance. Due to the uneven distribution of pore and steel fibre, the compressive strength and fatigue resistance of SSUHPC were inferior to that of UHPC prepared with freshwater river-sand. Firstly, this paper verifies the possibility of using seawater seasand to produce concrete with ultra high mechanical properties and durability. SSUHPC was slightly inferior to UHPC prepared from freshwater river-sand in mechanical properties, but it has more excellent durability characteristics. In view of these problems, the performance of SSUHPC can be further improved by improving the pore structure and fibre distribution.

The performance difference of mechanic properties and durability between SSUHPC and FRUHPC was systematically studied, and the mechanism of performance difference between the two kinds of concrete materials were revealed, which lay a solid theoretical foundation for the utilization of sea sand resources and the promotion of seawater seasand concrete.