International Concrete Abstracts Portal

A new type of admixtures for cement-based materials presented in this work is based on silane-modified acrylic polymers prepared by emulsion polymerization of acrylic monomers and organofunctional silane precursor. The acrylic polymer chain was functionalized with organofunctional silane molecules to build an organic-inorganic polymer structure with terminal siloxane groups. The advantage of this type of polymers over already known polymer modifiers for concrete and mortars is the ability to act as a coupling agent between different phases in the cementitious system. The presence of siloxane groups enables strong chemical interaction among mineral phases of inorganic matrix (cement, aggregate) and direct chemical bonding of organic polymer chain to inorganic phases of the cement based material. The influence of silane-modified acrylic latex admixture on the properties of cement paste and mortar was evaluated and compared to unmodified acrylic latex. Mortars modified with this type of hybrid inorganic-organic polymers showed improved physical-mechanical properties like higher mechanical strength, better adhesion to the substrate, lower shrinkage, better thermal conduction and better resistance to different sources of corrosion.

The knowledge of the concrete condition and monitoring of on-going deterioration processes are key factors for the management of concrete structures. Traditional assessment often remains limited and qualitative. This paper presents a new methodology based on radar tomography to estimate the water distribution in concrete, and therefore to assess indirectly the concrete condition. It aims at providing effective nondestructive procedures for engineers and structure managers. Work was conducted on a hydraulic structure suffering from alkali-aggregate reaction. Six boreholes were drilled to allow for core recovery and radar downhole measurements. Borehole radar antennas of 100 MHz central frequency were used for crosshole tomography. Radar data pointed out a high attenuation (high electrical conductivity), corroborated with the core testing. Both travel time and amplitude tomography needed to be carried out for an accurate determination of the dielectric permittivity. The Complex Refractive Index Model (CRIM) was used to relate the permittivity to the volumetric water content. The tomographic calculations were done using an algorithm based on geostatistical methods and stochastic simulations, allowing to draw probability maps of the volumetric water content. Results indicate that the overall volumetric water content is moderately high (0.15), and that some zones have high water content (above 0.2). These results will be used in the maintenance program of the structure.

Archaeological excavations inside Our Lady’s Basilica at Tongeren (Belgium), one of the most beautiful religious monuments in Belgium, are made possible through an adequate consolidation of the columns masonry foundations. The project includes a large archaeological excavation of the central nave up to a depth of more than three meters. To prevent instability of the columns, the foundation masonry is injected with a hydraulic grout. For the preservation of the archaeological remains, possibly available in the soil, the penetration of the grout into the layered soil must be prevented. Specific properties of the grout are thus required. The fluidity of the grout must be sufficient during injection, but has to decrease rapidly after a pre-determined period. Combined with an effective injection procedure, only the foundation masonry will be filled. The archaeological artifacts will thus be preserved. The grout has to be stable and bleeding must be under control. The compressive and bending strength must be sufficient and secured in time. The injectability of the grout in the foundations must be assured. The development of an appropriate grout for the injection of the columns foundation masonry will be described in this paper. The selections of the grout composition, as well as the design of an effective injection procedure are based on laboratory and on site tests. It is demonstrated that a grout containing a mixture of slaked lime and hydraulic cement performed excellently within the preset boundary conditions.

Self compacting concrete (SCC) is a new kind of concrete that combines a high flowability and a high segregation resistance obtained by a large amount of fine particles or the presence of a viscosity modifying agent and the use of superplasticizers. As self compacting concrete does not need external compaction, the pore structure, and more specifically the amount of capillary pores, is not influenced by the compaction method. These capillary pores play a very important role in the transport of water and gases in concrete and are of major importance for the understanding of degradation mechanisms. In order to verify the correlation between the transport properties and the capillary pores, tests were carried out. Water and gas permeability, capillary absorption, carbonation and chloride penetration tests were performed on 11 self compacting concrete mixtures and 1 traditional concrete mixture. The selection of the mixtures is made in order to consider some important parameters like the cement/powder and water/cement ratio, the amount of water, the amount of powder and the type of filler(limestone filler with two different grading curves). The amount of capillary pores was calculated by the method of Powers. The calculated values were compared with the test results and gave very good correlations.

It is well known that, in comparison with normal (usual) concrete, self compacting concrete (SCC) shows higher shrinkage because of the higher volume of binder, inevitable for achieving high fluidity and a good cohesiveness of the fresh concrete. It is necessary to avoid crack formation caused by drying or autogenous shrinkage as cracks could serve as flow paths and ingression zones for gases and salts or favour leaching. In order to diminish this negative effect of SCC’s, mixture concepts for the formulation of a shrinkage reduced SCC were developed. Different factors influencing the shrinkage behaviour are discussed. The effect of replacing cement by high volume of pozzolanic or inert additives as well as the effect of different shrinkage reducing admixtures (shrinkage reducing agents - SRA) was examined. Furthermore an optimization of the grain size distribution was evaluated. The measuring setup consisted of different methods, most important the measurement of free and restrained shrinkage (ring test) on mortar and concrete specimens. It could be shown, that through a significant reduction of the cement amount, accompanied by an effective shrinkage reducing admixture a massive shrinkage reduction of SCC’s in the range of 50% to 60% can be achieved.