Pump is a kind of effective concrete transportation means, can improve working conditions, reduce labor, improve construction efficiency, especially for the site of stenosis and obstruction of the construction site, as well as the mass concrete structures and tall buildings. Pumping concrete for pouring quantity in our country have been increasingly grow in quantity, commodity concrete in large and medium-sized city pumping rate amounts to 60% above, some even higher. High performance concrete construction mostly uses the pumping technology, choose a good pumping agent are also essential factors.
Concrete pumping concrete have greater mobility, and for a long time to maintain this performance, namely little slump loss, viscous good, concrete segregation, no bleeding, to do this, by adjusting proportion of concrete is not enough, must rely on the concrete admixture, especially concrete pumping agent. Single component admixture is difficult to satisfy the pumping concrete admixture on performance requirements, common pumping agent is a variety of admixture of composite products, its main components:
( 1) a water reducing component: ordinary water-reducing agent, water-reducing agent and high performance water-reducing agent can be used as pumping agent, water reducing component, as the engineering of concrete pumping admixture water reducing rate depending on requirements. When necessary, can also be used in several kinds of superplasticizers. Some high performance water-reducing agent and high performance water-reducer itself has a controlling concrete slump loss function, can be preferred.
( 2): retarding component in the preparation of pumping agent composition, although some water reducing agent to reduce concrete water binder ratio, but the loss of concrete slump faster, not conducive to the pump, the pumping agent adding appropriate amount of composition of the retarder, can control the slump loss of concrete, in favor of pump. In hot weather, even more important. Generally retarding superplasticizer is in a variety of high efficiency water reducing agent and adding proper quantity of retarder and other components, so that it conforms to the standard and the requirement of the project. A variety of high efficiency water reducing agent, in the normal volume, on cement setting time of concrete without apparent effect, sometimes in high volume when in use, the concrete setting and hardening time will also have more extended, played the role of retarder superplasticizer.
( 3) lubricant components: lubricant components in the transportation pipe wall to form a lubricating film, reduce the concrete conveying resistance, in order to reduce pumping pressure.
( 4): pneumatic components in pump concrete amount to join the air entraining agent, can prevent the segregation and bleeding. Air entraining agent to introduce a large number of small bubbles in the mixture stability, similar to the effect of bearing balls, these bubbles makes the particle movement more freely, can increase the mixture of plasticity. Bubble sand gradation can also play a complementary role, i.e. reducing sand grading effects.
( 5) thickening fractions: according to functions in concrete can be divided into the following categories:
Of natural and synthetic water-soluble organic polymers, these additives can improve the mixing water viscosity. This kind of material has a cellulose ester, epoxy ethane, alginate, carrageenan, polyacrylamide, hydroxyethyl polymers and polyvinyl alcohol.
The adsorption on the surface of cement particles of water-soluble organic flocculant, due to promotion of particle interactions and improve the adsorption viscosity, such substances including carboxyl styrene copolymer, synthesis of multicomponent electrolyte and natural water sol.
The various organic substances can improve the adsorption force of particle interactions, and at the same time in cement paste provides a supplemental ultrafine particles. The material includes paraffin emulsion, polypropylene and other polymer emulsion.
The large surface area of the inorganic material, this kind of material can improve the water holding capacity of concrete mixture. This class of substances including fine diatomite, silica, asbestos powder and other fibrous materials.
The inorganic material, this kind of material for mortar provided complementary fine particles, this class of substances including fly ash, kaolin, diatomite, untreated or calcined volcano ash material and a variety of powder.
Composite pumping agent composition, should be based on the specific circumstances and choice, not necessarily containing the composition.