Papers by Sandro Quispesivana Torres
Chlorides have been reported to be present in several field cases where thaumasite attack has occ... more Chlorides have been reported to be present in several field cases where thaumasite attack has occurred. However, no published systematic research dealing with the role of chloride in the thaumasite form of sulfate attack could be found in the literature. This research project has been designed through a comprehensive experimental programme to address this issue. This investigation studies the following: the formation of thaumasite in long-term exposure of carbonated systems to sulfate environment; whether or not the presence of chloride affects the thaumasite form of sulfate attack (TSA); the effect of long-term and short-term carbonation on the precipitation of thaumasite; the composition of thaumasite formed in chloride containing solutions; the chloride binding capacity of thaumasite-affected cement matrix; and the use of metakaolin to prevent TSA in carbonated mortar. Mortar samples were cast using siliceous sand and Portland cement replaced by different amounts (0,5 and 15%) of limestone filler, and by 10% metakaolin. Mortar cubes were subsequently stored in deionised water, magnesium sulfate solution, combined sulfate and sodium chloride solution and simulated seawater at 5°C and 20°C. Long-term specimens consisted of Portland cement mortars containing 15% limestone filler, which were exposed to atmospheric carbonation at 5 and 20°C for 5 years, were also immersed in these salt solutions at both temperatures. The mortar cubes were examined regularly every month, and the results of visual assessment recorded. The mineralogy of the deteriorated products was determined by x-ray diffraction (XRD), infrared spectroscopy (IRS). The pH of the solutions was also measured periodically. The composition of the thaumasite and the deteriorated cement matrix was assessed by means of the determination of the unit cell parameters of the crystal, by quantitative infrared spectroscopy (IRS); scanning electron microscopy (SEM); backscattered 1.2. Structure of the thesis 3 2. Chapter Two 5-2.4.4 The use of metakaolin replacing cement to prevent TSA 30 2.5 Concluding remarks iii 3 Chapter Three 34 Experimental Programme 3.1 Introduction 34 3.2 Experimental design 34 3.3 Materials 3.1.2 Characterisation 3.4 Mortar mixes and casting 3.5 Long term samples 38 3.6 Test Solutions 3.7 Visual inspection 3.8 Mass change 3.9 X-ray diffraction and Infrared spectroscopy sample preparation 3.9.1 XRD 3.9.2 Infrared Spectroscopy (IRS) 3.10 Scanning Electron Microscopy and X-Ray Microanalysis 3.11 pH changes 46 3.12 Statistical analysis 46 4. Chapter Four 48 Microstructure of 5-Year Old Mortars Containing Limestone Filler Damaged by Thaumasite 4.1 Abstract 48 4.2 Introduction 49 4.3 Experimental Work 50 4.4 Results and Discussion 51 4.2.1 Control OPC Mortar 51 4.2.2 Mortar with 5% limestone filler 55 4.2.3 Mortar with 15% limestone filler 57 4.2.4 Mortar with 35% limestone filler 61 4.2.5 Progress of TSA as a function of limestone content and period of exposure 64 4.5 Conclusions 65 iv 5 Chapter Five 66 Performance of Limestone Filler and Metakaolin Containing Portland Cement Mortars under Combined Chloride and Sulfate Exposure 5.1 Abstract 5.2 Introduction 5.2.1 Evidence to suggest that chloride plays a role in TSA A. Field cases B. Laboratory studies 5.2.2 Summary 5.3 Res ults 71 5.3.1 Visual Assessment 72 A. Up to 12 weeks 72 B. After 24 weeks C. After 44 weeks D. After 53 weeks E Seawater 81 F. Long term specimens 82 5.3.2 Mass loss in salt solutions 85 5.3.3 Mineralogy of deteriorated products 88 A. X Ray Diffraction (XRD) 89 B. IR Spectra 102 5.3.4 Effect of combined chloride and sulfate on the pH 111 A. 15% Limestone Filler 113 5.4 Discussion 122 5.4.1 Evidence suggesting a detrimental role for chloride in thaumasite formation 122 5.4.2 The effect of carbonation on TSA 125 5.4.3 The effect of chloride in the thaumasite form of sulfate attack in seawater 125 5.4.4 The use of metakaolin to prevent TSA 126 5.4.5 Effect of chloride on the pH profile in the presence of carbonates and sulfates 127 5.4.6 Mechanism by which chlorides affect TSA 129 5.5 Conclusions 134 V 6. Chapter Six 137 Effect of Combined Chloride and Sulfate on TSA: Microstructure and Micro-Analytical Results 6.1 Abstract 6.2 Introduction 138 6.3 Results 6.3.1 Microstructure of TSA in 15%LF samples in salt solutions at 5°C 142 A. 15% limestone filler in 0.60% S04 at 5°C 142 B. 15% limestone filler in 0.60% SO4 and 0.50 %Cl' at 5°C 145 C. 15% limestone filler in 0.60% SO'and 1.0% C1 at 5°C 148 D. 15% limestone filler in 0.60% SO 4-and 2.0% Cl' at 5°C 150 6.3.2 Characteristics of thaumasite in salt solutions A. Energy Dispersive X-ray 152 B. Quantitative X-ray microanalysis 156 C. Unit cell parameters 159 D. Infrared Spectroscopy (IRS) E. Sumary 177 6.3.3 Chloride binding capacity of Portland cement mortar containing limestone filler in salt solutions A. 15% limestone filler in 0.60% SO42' at 5°C B. 15% limestone filler in 0.6% SO4 and 0.5 %Cl' at 5°C 180 C. 15% limestone filler in 0.60% SO4 and 1.0% Cl' at 5°C D. 15% limestone filler in 0.60% SO4 and 2.0% Cl at 5°C 184 6.3.4 Chloride and magnesium profiles in 15%LF samples in salt solution at 5°C 187 A. 15% limestone filler in 0.60% S04at 5°C 187 B. 15% limestone filler in 0.60% SOäand 0.5 %Cl' at 5°C 189 C. 15% limestone filler in 0.60% SOäand 1.0% Cl' at 5°C 192 D. 15% limestone filler in 0.60% SO4and 2.0% Cl at 5°C 193 6.4 Discussion 196 6.4.1. Microstructural features of TSA in mortars containing limestone filler immersed in combined sulfate chloride solutions at 5°C 196 6.4.2 Effect of chloride on the composition of thaumasite 197 A. EDX/ X-ray microanalysis 197 B. Unit cell parameters 198 C. IRS 201 6.4.3. Effect of chloride on the chemical alterations of cement matrix due to TSA 202 A. Silicon profile 203 B. Aluminium profile 206 C. Sulfate profile 207 D. Chloride and magnesium profiles in mortar containing limestone filler immersed in combined sulfate and chloride solutions at 5°C. 210 6.5. Conclusions 213 V1 7. Chapter Seven Effect of Combined Chloride and Sulfate on TSA: Overall Discussion 7.1 Discussion 216 7.1.1 The effect of carbonate content on the microstructure changes in Portland cement mortars to TSA 7.1.2 The effect of atmospheric carbonation on the formation of thaumasite 7.1.3 The role of chloride in TSA: Damage assessment, characterization of deterioration products and main factors 220 7.1.4 The use of metakaolin in mortar containing limestone filler to prevent TSA221 7.1.5 Composition of thaumasite in the presence of chlorides 7.1.6 Chloride binding capacity and interaction in thaumasite attacked Portland cement matrix 7.1.7 Effect of pH on TSA 7.1.8 Mechanisms by which chloride affect thaumasite precipitation in Portland cement A. Carbonate system 226 B. Silicate system C Catalytic role of chloride in thaumasite formation 230 D. Summary 232 E. Damage assessment 235 8. Chapter Eight 237 Overall Conclusions 8.1 Overall Conclusions 237 8.2 Recommendations for future research References
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Papers by Sandro Quispesivana Torres