Study On The Performance Of Alkali-activated Slag Cement Under Seawater Corrosion

It is very helpful of investigating the anti-seawater corrosion performance of alkali-activated slag cement (ASC) to expand the use range of ASC and explore new ways of improving the durability of marine concrete.In this paper, the high strength ASC was prepared on the basis of optimizing the affects of various factors on the strength of ASC. Through drying cycle and long-term immersion dip, the properties of ASC in wet-dry alternation and under long-term seawater soak conditions were investigated, and were compared with performance of Portland cement (PC). On this basis, the mechanical properties and seawater corrosion resistance properties of ASC with mineral admixture such as fly ash and steel slag, etc. introduced were discussed. The mechanism of resistance to seawater erosion of ASC was studied with XRD, SEM and energy spectrum analysis.The results showed that: If the content of 10%～20% sodium silicate was blended with the modulus of 0.8～1.6, the 28-day bending strength of ASC reached to 5.5～8.5Mpa,and the compressive strength reached to 70～100MPa. When the modulus was 1.2 and the content of sodium silicate was about 16%, the highest strength of ASC was obtained; But even at smaller sodium silicate modulus and smaller dosage, the strength of ASC still arrived a higher value. With the lowering of water-cement ratio, the strength of ASC increased, and the strength development was accelerated also. The strength of ASC decreased after fly ash or steel slag was added; but the strength decrease little and the cement was still able to meet the strength of grade 52.5 if the content of fly ash or steel slag was within 20%.Under the corrosion of 5 times-concentration of artificial seawater, the surface of PC mortar peeled off very quickly and had a great occurrence of cracks, while the surface of ASC mortar flaked very little and the test blocks were still in good condition after 70 days'corrosion. The bending and compressive strength of PC mortar decreased by 50% after 70 days'corrosion, while the flexural strength of ASC mortar increased, and the compressive strength keep the same as the initial. The strenth of ASC can still achieve strength grade 52.5. The seawater-resistant quotiety of ASC outclassed PC greatly. After mixed with 20% fly ash or steel slag, the performance of anti-seawater corrosion of ASC increased. XRD tests showed that only NaCl crystal but no other corrosion products generated in ASC test blocks after seawater erosion. The bending strength of ASC was increased substantially and the compressive strength was also increased slightly after soaking in seawater for 6 months. ASC had an excellent performance under seawater corrosion because of its compact structure with fine pores and inert hydration products.