Special additive for higher water contents
The persistent balance between a too large and a too small amount of water in the course of manufacturing of concrete products is finally made easier. With the product Murasan Hydrotech 800 a new special additive has been developed for quality improvement in manufacturing of concrete products, which ensures a sufficient strength of newly demolded concrete elements despite vigorous fluctuations of the water contents.
Whereas the ready-mixed concrete and precast concrete industry predominantly makes use of plasticized and free-flowing concrete, concrete products, on contrary, are precast elements which are manufactured in automatic large-scale production. But, a sufficient strength is necessary so that the newly demolded concrete elements keep their shape. In this context one speaks about “green compressive strength” which is achieved through the mixture setup and intensive compaction in accordance with the principles of soil mechanics. A good green compressive strength is the pre-condition for a sufficient “green strength”, which is also necessary for the dimensional accuracy.
For concrete products therefore so-called earth-moist mixtures are generally applied in contrast to classical concrete technology. The low overall water contents caused by production partially leads to a water – cement ratio of less than 0.4, which means that the amount of water is not even sufficient for hydratizing the cement completely. For this reason, additives are requested and required allowing to increase the water contents.
The new additive Murasan Hydrotech 800 designed for the improvement of earth-moist concretes has now been launched by MC-Bauchemie as a special additive. It has been adjusted to meet the requirements of the concrete products industry. The effectiveness of the product is achieved on a chemical and physical basis.
The interrelationship among water contents, compaction energy, green compressive strength and the properties of hardened concrete of earth-moist concretes and the concrete products made of the same have been investigated already in the 60s and have been described in numerous publications, above all by H.-J. Wierig. If the water contents of a mixture is successively increased thus the green compressive strength grows at first under the condition of an equal compaction energy. This is the so-called “dry branch”. If the green compressive strength achieves a maximum value at a certain water contents it starts decreasing once again („wet branch“).
The investigations of Wierig show however that the 28-day compressive strengths on the “dry branch” decreases considerably. The decrease of the water impermeability is even more drastic resulting in a sharp reduction of the freeze-thaw resistance as well as the resistance against chemical impacts and a raise of the tendency to effloresce. By increasing the compaction energy the concrete may become denser, however the green compressive strength improves only by decreasing the water contents and/or increasing the binding agent contents.
Murasan Hydrotech 800 now allows to add that much water to earth-moist concrete mixtures that concrete products may safely be manufactured in the range of the “wet branch”. This is possible without any negative impact on the green strength.
First experiences gained in the production of, e.g., paving blocks, garden design elements or concrete pipes show that it is reasonable and possible to increase the amount of water between 5 and 15 liters per cubic meter of concrete. With the aid of Murasan Hydrotech 800 a better compaction of the fresh concrete is achieved as well as a very good surface quality of the concrete elements. Owing to the increased amount of water, the binding agent is used more effectively and the properties of the hardened concrete are sustainably improved. The freeze-thaw resistance grows and the tendency to effloresce declines.⇥■
