Fracture Toughness and Fracture Surface Morphology of Concretes Modified with Selected Additives of Pozzolanic Properties

Janusz Konkol

doi:10.3390/buildings9080174

Abstract

Modern methods of designing and testing concrete must be extended to appropriate material engineering approaches. It is then crucial to link the properties of concrete with its structure described in a quantitative way. The aim of the article was to present the results of research on concretes modified with three additives: Silica fume (SF), activated fluidal ash (FA), and metakaolinite (MK). The concretes were tested for compressive strength, fracture toughness (determining critical stress intensity factor KIcS and elastic modulus E). Also, stereological and fractal tests were performed. The research program covered three separate experiment plans, adopting the water/binder ratio and the additive/binder mass ratio as the independent variables. The results of experiments and their analysis proved a statistically significant relationship between fracture morphology (fractal dimension D) and concrete composition and fracture toughness. A higher fractal dimension was found in concretes with a higher content of cement paste and a lower content of additive. No significant effect of the type of additive used in the above dependence was found. An original method enabling the determination of mechanical properties of concrete with no need for destructive testing has been developed.

Highlights

The specific nature of tests on fracture toughness makes them non-typical and used infrequently compared with the common experiments on compressive strength
An example of how stresses change in concrete is illustrated by the result of tests done by Dantu [1]
Tests were performed for three additives separately: Silica fume (SF), activated fluidal ash (FA), and metakaolinite (MK)

Summary

Introduction

The specific nature of tests on fracture toughness makes them non-typical and used infrequently compared with the common experiments on compressive strength. The significance of fracture toughness tests is indisputable. The state of stress in concrete elements is not restricted merely to compression. An example of how stresses change in concrete is illustrated by the result of tests done by Dantu [1]. It turns out that in plain concrete, the stresses occurring at the contact between aggregate grain and cement matrix can be twice higher than the average stresses adopted in the design. The variable stress pattern, together with discontinuities in the concrete structure, proves the necessity of research on fracture toughness

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