Durability of Concrete. New Admixtures for Quality and Durability Improvement of Concrete

摘要

The lifetime of any concrete structure is limited by any environmental attack, engineering design, concrete composition and application. The attack on the concrete is initiated from outside, and any 'failure' of the surface properties can be apossible start for the deterioration of the whole structure. The surface quality of concrete is partially controlled by the mix design and the hydration process of the cement. Concrete needs water for the chemical reaction and produces significant heat while hydrating. Expansion and contraction due to temperature changes can cause serious cracks. The possible evaporation of excess mixing water is a function of time, relative humidity and wind exposure. The drying out of a nonprotected concrete surface is a well-known phenomenon which contributes to the reduction of surface quality and is the major factor for drying shrinkage. Bonding to this surface is minimised, and shrinkage cracking with a low degree of hydration is common. Here will now be described a possible way of reducing these negative influences by means of the addition of a specially designed admixture to the fresh concrete at the batching plant. The addition of this admixture seems to overcome the compromise between a high water-cement ratio and too little water at the surface. Both decrease the lifetime of the whole concrete structure.