No abstract

The present study concerns hydrophobic surface treatments with silane-based coating on concrete surfaces against external ionic transport. The nano-modification and organic–inorganic modification were carried out on it and applied to the mortar matrix and concrete matrix. Lithium-based protective coating (PC1, PC2), nano-modified coating (NC1, NC2) and organic–inorganic composite coating (OL1) were prepared. The salt erosion resistance of the mortar matrix and concrete matrix was tested, compared with the blank group and the market. The test results found that the organic–inorganic modified OL1 and LC1 coatings have the greatest influence on the chloride penetration resistance of the mortar matrix, in which the chloride penetration depth of 28 days is reduced by 73.03% and 63.83%, respectively, compared with the blank group. The rate of mass change of the blank group, PC1 and PC2 coatings, and NL1 and NL2 coatings were 0.17%, 0.08%, and 0.03%, respectively. The result demonstrated that the lithium-based coating could effectively delay the penetration rate of chloride ions and sulfates into the mortar, and the nano-modified properties could improve the salt resistance. The scanning electron microscopy (SEM) showed that coating treatment would promote the secondary hydration of cement-based materials, by reducing the content of Ca(OH)2 in hydration products of cement-based materials and producing C-S-H gel, which is conducive to strength enhancement and pore refinement. The nano-component would promote the reaction degree, while the organic–inorganic coating would have the respective advantages of the two components.

Using dehydrated silt soil as a raw material to produce ceramsite for ceramsite concrete blocks is a promising approach from both environmental and economic aspects. In this paper, flocculant polyacrylamide (PAM) was investigated to dehydrate the silt, and the optimal dosage of PAM was found to be 0.8 mol/L. The dehydrated silt was then fired to obtain ceramsite, which was subsequently used to prepare ceramsite autoclaved concrete blocks (CACB). The compressive strength of the blocks was tested and compared with that of ordinary autoclaved concrete blocks (ACB) and Nano-CaCO3 autoclaved concrete blocks (NACB). The results showed that the addition of ceramsite or Nano-CaCO3 can improve the compressive strength, with an increase of 44.4% and 55.6% at 7 d, respectively, compared with the autoclaved concrete block.

The effects of Nano-CaCO3 on the physical, mechanical properties and durability of cement-based materials were investigated in this paper. The mechanical property, durability and SEM microscopic tests of test blocks with different Nano-CaCO3 content were carried out. Results showed that Nano-CaCO3 could improve the flexural strength, compressive strength and impermeability of cement-based materials. When the content of Nano-CaCO3 is 2.0%, the strengthening effect of Nano-CaCO3 on the cement-based materials was optimized, and the flexural strength of cement-based materials after 3 d, 7 d and 28 d increased by 12.6%, 18% and 32.4%, respectively, compared with the reference group. When the content of Nano-CaCO3 exceeded 2.0%, the flexural strength of cement-based materials begins to decline with the increase of Nano-CaCO3 content. Similarly, when the content of Nano-CaCO3 reached 2.0%, the impermeability of the cement-based materials was also optimized, and the permeability height of the base group could be increases by 41.4%. At the early stage of hydration, the exothermic rate of cement with 2.0% Nano-CaCO3 content was higher than that of other contents. When the content of Nano-CaCO3 increased from 0 to 2.0%, the hydration exothermic rate increased gradually with the increase of Nano-CaCO3 content.