In the process of construction, cracks will also occur due to water evaporation and untimely maintenance, such as shrinkage cracks, expansion cracks, moving cracks and structural cracks, especially mass waterproof concrete, which is more likely to cause structural cracks and leakage if it is not well controlled. The key technology of waterproof concrete is how to control the cracks in the construction process or to control the cracks within the allowable range, instead of unilaterally emphasizing the increase of cement dosage and the improvement of concrete compressive strength.
In recent years, the key to the development of waterproof concrete technology is "the combination of self-waterproofing and waterproof and drainage of concrete structures", with the emphasis on "preventing concrete cracking". The means is to "add high-quality fly ash, silica fume, water reducer, expansion agent and other additives, and use fiber in the formula to increase the compactness of concrete and reduce the number of cracks".
Specifically, strictly control the compressive strength grade of the main structure, optimize the mix proportion design of concrete, reduce the dosage of cement, increase the proportion of high-quality fly ash or other additives, strictly control the slump of concrete, and pay attention to reducing the slump and strengthening the maintenance after formwork removal.
Waterproof mortar has strong bonding strength and is often used for waterproofing the surface of underground engineering structures. There are many kinds of waterproof mortar. Early use of ordinary cement mortar, with different proportions of plain ash and mortar layered staggered, forming a continuous closed waterproof layer. With the application of additives in cement mortar, ordinary cement mortar has been replaced by waterproof mortar mixed with various additives, waterproofing agents and polymer emulsion, and the construction procedures have been continuously simplified and the technical indicators have been continuously improved.
In recent two years, we mainly developed polymer (dry powder) waterproof mortar, such as polymer cement, QL- 1 1A and QL-1B polymer waterproof mortar, PCM-480a polymer waterproof mortar, and waterproof mortar mixed with FS 102 waterproof agent. Their * *.
In the aspect of additives used in rigid waterproof materials, there has also been great development. For example, in September 2006, Beijing Urban Construction Science and Technology Promotion Association evaluated a new series of waterproof concrete and waterproof mortar additives, including FS 10 1 and FS 102. The main component of this additive is a liquid solvent extracted from sulfur and sand by calcination at a high temperature of 1200℃, which naturally dissolves with water.
The main characteristics of FS 10 1 and FS 102 waterproofing agents are: they have good control ability on shrinkage cracks of waterproof mortar and waterproof concrete; For the super-long slab of concrete structure, the setting of post-pouring belt and strengthening belt can be cancelled or reduced, and concrete can be poured continuously; No special requirements for construction conditions, simple construction, no pollution, environmental protection and safety.
The reaction mechanism of this admixture is that it reacts chemically with cement hydration sediment to generate gel and crystal, which fills tiny pores of concrete, blocks and cuts off capillary channels, and inhibits water from infiltrating into concrete, thus effectively controlling the generation of shrinkage cracks and improving the impermeability of concrete or mortar.
It is one of the most effective methods to reduce the internal temperature rise caused by hydration heat of mass concrete and prevent temperature cracks in the structure. After adding a certain amount of fly ash into mass concrete, it can increase the compactness of concrete, improve the impermeability, improve the workability of concrete, reduce the final shrinkage value and reduce the amount of cement.
Admixtures can be selected from the following aspects. UFA expansive agent can replace cement in equal amount, on the one hand, it can ensure the compactness of concrete, on the other hand, it can generate pressure inside concrete to offset some tensile stress in concrete, add and subtract water reducing agent, ensure a certain slump, postpone the peak period of hydration heat, improve the workability of concrete and reduce the water cement ratio, thus achieving the purpose of reducing hydration heat.