G . Hüsken ; H . J . H . Brouwers Experimental and Theoretical Study of Earth - Moist Concrete

Earth-moist concrete mixes are the starting substance for the mass production of concrete products like pipes, slabs, pavement stones and curb stones. The working properties of earth-moist concrete (EMC), caused by its dry consistency, are advantageous. So, in comparison to normal-weight concrete, the consistency of EMC allows for direct stripping of concrete products after filling and vibrating the molds. As a result, short processing times of the production process can be realized. Further examples for concrete with stiff consistency are roller compacted concrete (RCC) which is stiff enough to be compacted by vibratory rollers. RCC is used for any type of industrial as well as heavy-duty pavements or in combination with bigger aggregates as roller compacted concrete for dams (RCD). Traditional earth-moist concrete mixes for concrete products are characterized by high cement contents between 350 kg and 400 kg per m concrete and a low content of fine inert particles. They have a low water/cement ratio (w/c < 0.4) combined with a very stiff consistency and a high degree of compactibility. Furthermore, the degree of consistency of EMC is defined by Häring as free-flowing /5/. As a result of low water/cement ratio, high compressive strength values are achieved by earth-moist concrete mixes and durability is improved compared to ordinary concrete. However, despite these positive properties there is potential for improvements. Possible fields for improvements are in the workability, compactibility, green strength, packing density and a reduction of the cement content by using fly ash, limestone powder or other possible powders as a substituent, such as fine stone waste products, in order to increase the content of fine inert particles. This replacement of primary raw materials by secondary waste materials constitutes an environmental and financial advantage. An optimization of the packing and the ratio of water in voids, in consideration of the material properties of the available raw materials, can lead to an increase in the green strength of fresh concrete and to higher compressive strength values of the concrete in hardened state. With an increase in compressive strength, the amount of cost-intensive cement can be reduced by using cost-saving powders as substituent. These powders, such as fly ash, will also influence the compressive strength of the hardened concrete positively. This enormous potential for optimization will be the starting point for further investigations into the development of EMC for the innovative production of concrete. At first, the packing of all aggregates will be investigated as an optimum packing is the key for a good and durable concrete.