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Pozzolanic Activity of Silicon Dioxide
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The aim of this bachelor's thesis is to investigate and identify the present status of resources with dominant amorphous silicon dioxide content and summarize feasible test methods to assess pozzolanic activity. The use of pozzolan as a partial replacement of Portland cement reduces the carbon dioxide emitted per tonne of product and can also improve various physical properties of the resulting cementitious composites. Assessment of the pozzolanic activity of cement replacement materials is increasingly important because of the economic sustainability of cementing materials. The pozzolanic activity of wheat straw ash, silica fume, nanosilica, two diatomites, glass powder and expanded perlite have been investigated and compared using the strength activity index test, the modified Chapelle test and the pozzolanicity test in accordance with the European Standard EN 196-5. From an experimental investigation of seven different pozzolans, the following main conclusions can be drawn. In the case of an acid-base titration (determination of [OH–], the procedure specified in EN 196-5) is better to use Tashiro (mixed indicator) instead of required methyl orange, Tashiro changes color at the endpoint of a titration distinctly. Strength activity index: the procedure used was based on EN 450-1. In its current form, this procedure is misleading because of two other significant properties of the pozzolan, namely its density and its water-reducing/increasing capabilities. Based on the results of our experimental investigation, the current testing procedure is evaluated against an alternative in which the 25% pozzolan replacement for cement is performed on a volumetric basis and the volume fraction of water is held constant.
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Effect of colloidal silicon dioxide on selected properties of cement pastes and mortars
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The presented diploma thesis deals with the potential use of colloidal silica in cement composites. Investigation is focused primarily on selected properties of cement pastes and mortars with colloidal silica content. Two selected types of colloidal silica (particles with average size of 14 nm) have been used as a cement addition and partial replacement of cement, respectively. The experimental program for cement pastes with colloidal silica included tests for isothermal calorimetry (the study of cement hydration) and thermal analysis (determining the portlandite content). Hardened cement pastes have been studied through measurements of compressive strength. The microstructure was examined by scanning electron microscopy. Hardened mortars with colloidal silica have been studied through measurements of compressive strength, flexural strength, modulus of elasticity and fracture mechanics parameters. Fracture mechanics tests show that 5 % and 20 % addition of colloidal silica can enhance after 28 days of curing fracture energy up to 18,4 % and 32,7 %, respectively. For the compressive strength enhancing effect of colloidal silica, it was found to be more pronounced in the early age, while rate of strength gain can be lower than the control in the later ages. Our investigations revealed that the silica sol will coagulate immediately when the cement is mixed into the water containing sol. The ionic composition of pore fluid significantly influences the stability of colloidal silica and lead to their aggregation. After additional tests it has been found that small addition of calcium hydroxide greatly improved the compressive strength of the resulting cement pastes with colloidal silica content. Addition of calcium hydroxide in conjunction with modified cement paste preparation can enhance compressive strength after 3 days of curing up to 64,4 % in comparison with the blank paste.
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Effect of colloidal silicon dioxide on selected properties of cement pastes and mortars
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The presented diploma thesis deals with the potential use of colloidal silica in cement composites. Investigation is focused primarily on selected properties of cement pastes and mortars with colloidal silica content. Two selected types of colloidal silica (particles with average size of 14 nm) have been used as a cement addition and partial replacement of cement, respectively. The experimental program for cement pastes with colloidal silica included tests for isothermal calorimetry (the study of cement hydration) and thermal analysis (determining the portlandite content). Hardened cement pastes have been studied through measurements of compressive strength. The microstructure was examined by scanning electron microscopy. Hardened mortars with colloidal silica have been studied through measurements of compressive strength, flexural strength, modulus of elasticity and fracture mechanics parameters. Fracture mechanics tests show that 5 % and 20 % addition of colloidal silica can enhance after 28 days of curing fracture energy up to 18,4 % and 32,7 %, respectively. For the compressive strength enhancing effect of colloidal silica, it was found to be more pronounced in the early age, while rate of strength gain can be lower than the control in the later ages. Our investigations revealed that the silica sol will coagulate immediately when the cement is mixed into the water containing sol. The ionic composition of pore fluid significantly influences the stability of colloidal silica and lead to their aggregation. After additional tests it has been found that small addition of calcium hydroxide greatly improved the compressive strength of the resulting cement pastes with colloidal silica content. Addition of calcium hydroxide in conjunction with modified cement paste preparation can enhance compressive strength after 3 days of curing up to 64,4 % in comparison with the blank paste.
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|
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Pozzolanic Activity of Silicon Dioxide
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The aim of this bachelor's thesis is to investigate and identify the present status of resources with dominant amorphous silicon dioxide content and summarize feasible test methods to assess pozzolanic activity. The use of pozzolan as a partial replacement of Portland cement reduces the carbon dioxide emitted per tonne of product and can also improve various physical properties of the resulting cementitious composites. Assessment of the pozzolanic activity of cement replacement materials is increasingly important because of the economic sustainability of cementing materials. The pozzolanic activity of wheat straw ash, silica fume, nanosilica, two diatomites, glass powder and expanded perlite have been investigated and compared using the strength activity index test, the modified Chapelle test and the pozzolanicity test in accordance with the European Standard EN 196-5. From an experimental investigation of seven different pozzolans, the following main conclusions can be drawn. In the case of an acid-base titration (determination of [OH–], the procedure specified in EN 196-5) is better to use Tashiro (mixed indicator) instead of required methyl orange, Tashiro changes color at the endpoint of a titration distinctly. Strength activity index: the procedure used was based on EN 450-1. In its current form, this procedure is misleading because of two other significant properties of the pozzolan, namely its density and its water-reducing/increasing capabilities. Based on the results of our experimental investigation, the current testing procedure is evaluated against an alternative in which the 25% pozzolan replacement for cement is performed on a volumetric basis and the volume fraction of water is held constant.
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