Sulphate and ASR Resistance of Concrete Made with Calcined Clay Blended Cements

Abstract

This paper presents the results of several investigations concerning the durability of mortar and concrete with higher proportion of calcined clays in the cement part. For this purpose, different clays based on kaolinite, montmorillonite and illite were fired at optimum temperatures according to the strength contribution in cement. The raw materials were analyzed chemically (XRF) and mineralogically (XRD). The pore size distribution of the mortars was measured by mercury intrusion porosimetry. Cement pastes were produced in order to calculate the phase composition by XRD/Rietveld and to estimate the microstructure with SEM. The performance tests comprised investigations of the long-term behaviour in case of sulphate attack and alkali silica reaction respectively. The results show that the addition of the calcined clays are able to improve the concrete resistance against these exposures or at least doesn't affect it negatively compared to the control. It can be followed that the application of cements with higher percentage of calcined clays substituting clinker is not restricted to only slightly loaded concrete constructions.

Calcined Clay as Supplementary Cementitious Material

“…Trümer and Ludwig [ 188 ] put forward the thesis that one of the obstacles to the wider use of calcined clays in cement and concrete technology is the lack of information on the long-time behaviour of the concrete. They used clays of various mineralogical composition, which they subjected to the process of thermal activation and used in concrete mixtures as a substitute for 30% of the cement.…”

“…Calcined clay is a pozzolanic material which makes it possible to reduce the negative effects of alkali-silica reaction, which has been demonstrated in a number of studies [ 188 , 195 , 196 ]. This is one of the methods of preventing ASR, besides the use of low-reactivity aggregate [ 197 ].…”

“…The research showed that the chemical and mineral composition of the clay was crucial for the effectiveness of ASR mitigation. Trümer and Ludwig [ 188 ] tested the resistance of concrete with cement mixed with calcined clay to both ASR and sulphate attack. Three calcined clays containing as basic minerals, respectively, kaolinite, illite and montmorillonite after mixing with CEM I cement in a ratio of 30:70 significantly reduced the expansion of mortars and increased their resistance to sulphate attack.…”

Sulfate and Alkali-Silica Performance of Blended Cements Containing Illitic Calcined Clays

“…Partly substitution of alkali-rich portland cements by calcined clays improves the resistance of the respective concrete against sulfate attack and harmful ASR [3]. It is attributed to the pozzolanic reactivity that consumes the CH to produce C-S-H and C-A-S-H causing a denser microstructure due to the pore and grain size refinements [3,4]. To controlling ASR, metakaolinite has a very good performance suppressing the expansion.…”

Brittle Materials in Mechanical Extremes

“…A few works have demonstrated the peculiar behavior of brittle materials, such as concrete (see the book of Torrenti et al [ 1 ]), composite materials (see e.g., [ 2 ]), and ceramics (see e.g., [ 3 , 4 ]), especially if they possess special features such as pores or hard phases, or undergo microcracking. Microcracks, together with porosity, impart to such materials an exceedingly large strain tolerance (strain at failure), where the specimen is able to carry some (small) load even when it is fully fractured (thereby displaying residual strength [ 5 ]), excellent corrosion resistance [ 6 ], or extremely high thermal shock resistance [ 7 ]. In this sense, such materials behave similarly to metamaterials, where the meso-structure (at scales above the grain size) is as important as the material composition of the micro-structure (at scale below the grain size).…”