An investigation was executed into the applicability of self-compacting high performance fiber concrete in foundations. The applied concrete has a concrete cube strength of about 110 MPa and contains 60 kg/m³ hooked-end steel fibers (L_F = 30 mm, D_F = 0.38 mm). This publication consists of two parts: (1) Experimental assessment and verification of design rules and (2) assessment of fiber orientation and distribution. In the first part, experiments are described which were carried out to determine the pre- and post-cracking strength properties, the shear resistance of short beams, the anchorage length of rebars, and the shear capacity of foundation slabs supported on piles. The test results were used for a verification and extension of design rules for fiber reinforced concrete (FRC) found in the fib Model Code 2010. The application of the FRC developed can lead to substantial savings in concrete and reinforcing steel. In the present second part, cross-sections of two slabs and a beam of this testing series have been analyzed with regard to fiber orientation and distribution. An image analysis, executed on 111 concrete areas, indicates that a preferred fiber orientation could not be identified throughout the assessed elements. The data supports the conclusion of a good fiber distribution as well; a strong correlation was obtained for the data set of full images between measured and theoretical relation of fiber orientation and fiber density.@en

An investigation is carried out into the applicability of self-compacting high-performance fiber concrete (HPFC) in foundations. A concrete mixture has been designed with a concrete cube strength of about 110 MPa. The concrete contains 60 kg/m³ steel fibers. The properties of the HPFC developed are very suitable for structural applications, especially because the post-cracking tensile strength, provided by the fibers, is higher than the axial tensile strength of the concrete so that hardening in tension occurs after crack formation, often characterized by multiple cracking. This not only results in a high bearing capacity but as well in substantial durability. As a potential application foundation elements are considered. Experiments have been carried out to determine the pre- and post-cracking strength properties, the shear resistance of short beams with loads near to the supports, the anchorage length of reinforcing bars, and the shear capacity of pile caps. The results of the tests are used for verification of the applicability of the general design rules for fiber concrete, as found in the fib Model Code 2010, to the HPFC developed. The HPFC developed is characterized by high strength and ductility, is durable and self-compacting. The research program showed that the design of structures with the HPFC considered can be based on existing design rules with some extensions.

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Traditionally industrial foundation elements are manufactured using reinforced concrete. For these elements a lot of reinforcement is necessary as these foundation elements are usually loaded by the combination of large shear forces and bending moments. Moreover, splitting and spalling reinforcement is crucial to transfer the internal stresses as very large concentrated loads are present. Due to the combination of the different reinforcement requirements the production process of these foundation elements is complex and requires a lot of time and labor. Simplification of the production process for foundation works will result in a more effective execution and de-risking of the construction schedule. Therefore, the idea was born to use self-compacting high performance fibre reinforced concrete (SCHPFRC) reinforced with traditional steel only for bending. The steel fibres will take over the functions of all other types of traditional reinforcement, i.e. shear reinforcement, transverse reinforcement, skin reinforcement, minimum reinforcement and additional reinforcement required to control crack widths. To test the capabilities and the behavior under large concentrated loads of this SCHPFRC, two extensive test series are performed at the Magnel laboratory for Concrete Research at Ghent University. The first test series consisted of the development of a mix design for the SCHSFRC, 12 CMOD tests on SCHPFRC prisms, 6 full scale loading tests on SCHPFRC beams subjected to a concentrated load to test the shear resistance and 6 full scale loading tests on SCHPFRC slabs. In the second test series additional tests are performed to confirm the findings from the first test series, to investigate the influence of the steel fibers on the anchorage length of the steel rebars and to investigate the punching resistance and the three-dimensional load-transfer of the foundation elements in more detail. Based on the outcome of the experiments the applicability of SCHPFRC is evaluated and practical design guidelines are derived.@en

Traditionally industrial foundation elements are manufactured using reinforced concrete. For these elements a lot of reinforcement is necessary as these foundation elements are usually loaded by the combination of large shear forces and bending moments. Moreover, splitting and spalling reinforcement is crucial to transfer the internal stresses as very large concentrated loads are present. Due to the combination of the different reinforcement requirements the production process of these foundation elements is complex and requires a lot of time and labor. Simplification of the production process for foundation works will result in a more effective execution and de-risking of the construction schedule. Therefore, the idea was born to use self-compacting high performance fibre reinforced concrete (SCHPFRC) reinforced with traditional steel only for bending. The steel fibres will take over the functions of all other types of traditional reinforcement, i.e. shear reinforcement, transverse reinforcement, skin reinforcement, minimum reinforcement and additional reinforcement required to control crack widths. To test the capabilities and the behavior under large concentrated loads of this SCHPFRC, two extensive test series are performed at the Magnel laboratory for Concrete Research at Ghent University. The first test series consisted of the development of a mix design for the SCHSFRC, 12 CMOD tests on SCHPFRC prisms, 6 full scale loading tests on SCHPFRC beams subjected to a concentrated load to test the shear resistance and 6 full scale loading tests on SCHPFRC slabs. In the second test series additional tests are performed to confirm the findings from the first test series, to investigate the influence of the steel fibers on the anchorage length of the steel rebars and to investigate the punching resistance and the three-dimensional load-transfer of the foundation elements in more detail. Based on the outcome of the experiments the applicability of SCHPFRC is evaluated and practical design guidelines are derived.@en

This work aims at providing a better understanding of the mechanical properties of the reaction rim in the alkali-silica reaction. The elastic modulus of the calcium alkali silicate constituting the reaction rim, which is formed at the interface between alkali silicate and Ca(OH)2 in a chemically-idealized system of the alkali-silica reaction, was studied using nano-indentation. In addition, the corresponding calcium to silica mole ratio of the calcium alkali silicate was investigated. The results show that the elastic modulus of the calcium alkali silicate formed at the interface increased with the increase of the calcium to silica mole ratio and vice versa. Furthermore, the more calcium that was available for interaction with alkali silicate to form calcium alkali silicate, the higher the calcium to silica mole ratio and, consequently, the higher the elastic modulus of the formed calcium alkali silicate. This work provides illustrative evidence from a mechanical point of view on how the occurrence of cracks due to the alkali-silica reaction (ASR) is linked to the formation of the reaction rim. It has to be highlighted, however, that the simplified calcium-alkali-silicate system in this study is far from the real condition in concrete.

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This work is intended to provide a better understanding about the properties and roles of the reaction rim in an alkali-silica reaction. A simplified calcium-alkali-silicate system was created to simulate the multiple interactions among reactive silica, alkaline solution and portlandite near the aggregate surface during the formation and evolution of the reaction rim in an alkali-silica reaction. A transport barrier preventing the migration of calcium and silicate through itself was found on the interface between the alkali silicate and the calcium hydroxide. The barrier was mainly composed of calcium alkali silicate with silicon-oxygen organizations of Q2 and Q3 according to the results of 29Si nuclear magnetic resonance, the calcium to silica mole ratio ranging from 0.22 to 0.53 and the alkali to silica ratio ranging from 0.20 to 0.26 based the location of the elemental compositional analysis and the storage period of the system.@en