Lightweight porous concrete mainly includes foamed concrete and aerated concrete, with the characteristics of light weight, heat preservation and insulation, sound absorption and sound insulation, fire prevention and non-combustion, etc., it is a kind of new energy-saving insulation material widely used in modern buildings.However, due to its high porosity, large surface free energy, easy to absorb water and lead to the strength and insulation performance of the reduction, anti-freeze and thaw and durability of the poor.In particular, surface water absorption is easy to cause drying shrinkage rate rise, and the binding force of plastering mortar drops, resulting in wall empty drum, mildew, cracking and large area shedding, etc., seriously affecting the building
Beautiful wall and service life.Therefore, improving the waterproof performance of lightweight porous concrete becomes an urgent research topic.
Based on the existing research results, the water-proofing agent of lightweight porous concrete can be classified into inorganic, organic and inorganic organic mixtures according to the chemical composition.
Mechanism of action of water repellent
1. Silicone water-repellent agent
Silane or silicone water-repellent agent in porous concrete has been paid more attention by researchers at home and abroad.Silane or silicone with different substituents and structures have different waterproof effects.There are many kinds of organic silicon, but the main active ingredients are alkyl silanolates, alkyl alkoxy silane and alkoxy.
Methyl silicon alkoxide is the first generation of organic silicon waterproof material, is liable to be weak acid decomposition of CO2 in the air and water to generate insoluble in water under the action of methyl sodium silicate, mesh and concrete substrate reaction to form hydrophobic poly (methyl siloxane membrane layer, but due to the strong alkali conditions will generate silicon alcohol soluble in water, with waterproof moisture loss and lost.
Silane for waterproofing, usually refers to the number of carbon atoms n or more than 8 linear alkyl alkyl oxysilane.Silane's organic protective group, the r-group, hydrolyzes to form stable carbon-silicon bonds that bind to silicon atoms, creating a hydrophobic coating with low surface energy that prevents water from entering but allows water vapor to enter or leave the concrete.
Silicone emulsion is based on the reaction of active components with hydroxyl groups and other active groups on the surface of silicate porous materials to form a network waterproof film layer with water resistance.However, there are problems of short shelf life and poor stability of emulsion silicone water repellent.
2.Fatty acid salt water repellent
Fatty acid salt is a water-repellent agent. First, it is reactive. It contains water-resistant carboxylic acid group (-- COOH or -- COONa) and Ca+ in the mixture, which is complexed and deposited on the surface of the mixture.Second, non-reactive, active and effective substances are combined with the matrix and filled in the pores inside the concrete to reduce water channels and water absorption.
3.Paraffin emulsion waterproofing agent
Paraffin after surfactant emulsion formation of paraffin emulsion, emulsion paraffin molecules, after the blockage in the process of porous concrete hydration internal hole and grain to form package for the material, transformation of its surface from hydrophilic to hydrophobic, the hydrophobic membrane layer made of porous concrete water drops, reduce moisture to evaporate after leaving the pore, reduce the water absorption of porous concrete.
4. Water-based permeable crystalline water-repellent
Water-borne permeable crystalline water-repellent (DPS) is a kind of water-based water-repellent agent (DPS) that takes advantage of its own crystallization characteristics and rapidly penetrates into the surface layer after contacting with concrete materials, forming crystallization in the interior of pores and blocking the entry and flow of water molecules by capillary tubes.