Compressive strength estimation of sprayed concrete at early ages
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The sprayed concrete complies a construction technique that combines the placement and the compacting of concrete in only one process. This sort of concrete, which is widely used in underground constructions, requires a quick setting obtained by using set accelerating admixtures. Due to the function performed by these admixtures during the hydration process of the concrete, an analysis of its mechanical properties at early ages is essential. The European Standard ‘EN 14488-2:2007 - Testing sprayed concrete. Part 2: Compressive strength of young sprayed concrete' describes the indirect methods used to determine the compressive strength of the sprayed concrete at early ages. These are the penetration needle test and the stud driving method. The first one estimates the compressive strength until 1.30 MPa evaluating a force gradually applied so that a needle penetrates a certain distance. The second one estimates the compressive strength evaluating the penetration of studs shoot with a certain power and the force to extract them. This second method cannot be performed until the compressive strength of the sprayed concrete is around 2.50-3.00 MPa. Therefore a range of strength cannot be estimated. This range entails certain time in which the estimation of the compressive strength of the sprayed concrete is not possible. This communication aims to present the problem related with the estimation of the compressive strength of the sprayed concrete at early ages. Furthermore, it objects to give a solution for this problem adapting the maturity method for the spraying concrete. In other words, it tries to solve the problem using the relationship between the compressive strength and the evolution of temperature during the hydration of cement. Therefore, a wide experimental program was performed testing specimens produced with different types of cement and types of accelerators. The results obtained present the impossibility to estimate a certain range of compressive strength using the penetration needle test and the stud driving method. Furthermore, the analysis of the experimental results allows adapting the maturity method for sprayed concrete. Therefore, the relationship between the compressive strength and the evolution of temperature, which depends on the type of cement and accelerator, can be used to estimate the compressive strength of the sprayed concrete at early ages.
CitacióGalobardes, I. [et al.]. Compressive strength estimation of sprayed concrete at early ages. A: Congresso Brasileiro do Concreto. "Ações concretas para o futuro da construção em concreto no Brasil". Gramado, Rio Grande do Sul: 2013, p. 1-16.