The effect of inadequate compaction on compressive strength of concrete exposed to elevated temperature

Headnote

KEYWORDS

Inadequate compacting; Taguchi method; ANOVA; High temperature; Compressive strength.

Abstract. One of the important factors affecting the quality of concrete is the placement of fresh concrete inside the formwork. Inadequate compaction is a common problem in concrete technology. In this study, the effect of inadequate compaction on compressive strength and ultrasonic pulse velocity of concrete exposed to elevated temperature is examined. For this purpose, various compaction rates were applied during the casting stage of concrete in order to simulate various levels of inadequate compaction. Four different water-cement ratios (0.50, 0.40, 0.38, and 0.35) were selected. All concrete specimens were exposed to 450 or 900° C for one hour. The Taguchi approach was used to reduce the number of samples. The results were evaluated by the Analysis of Variance (ANOVA) method. Test results showed that inadequate compaction played a significant role, more than curing time, in the compressive strength after high temperature exposure.

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(ProQuest: ... denotes formulae omitted.)

1. Introduction

Concrete is a composite material having porous, composed of mineral aggregates in a cement matrix. The hydration reaction of cement occur a solid porous system. The porous system of concrete allows transport of water and other substances [1]. The pores of concrete are classified according to their size as air pores, capillary pores, gel pores, and compaction pores (affect durability) [2,3]. The gel pores, which are mostly 1.5-2.0 nm in size, do not influence negatively the strength of concrete. The role of these pores is to directly affect creep and shrinkage. On the other hand, capillary, air, and compaction pores are responsible for reductions in compressive strength and the Young's or elasticity modulus [4-8].

Concretes with higher water-to-cement ratios naturally contain more water than what is required for complete hydration of cement. This excess water causes voids known as capillary pores. Pores in concrete can also occur by inadequate compaction caused by poor workmanship (see Figure 1). This pore system is one of the most important properties of concrete because of its effects on carbonation and sorptivity [9].

High temperature is known to cause durability problems in concrete. Even though concrete is a noncombustible material, its internal structure deteriorates at high temperature. The type of...