For making concrete with high strength, quartz is one of the materials used as an aggregate in such a concrete.
Dear Ali,
Quartz is nearly always inert when used as aggregate (not fine powder as cement replacement material) in concrete. It means that it will not react at normal conditions. less reactivity, more controllable situation in concrete. That is the reason make it desirable for concrete as well as its hardness.
At room temperature, SiO2 in all modifications is almost inert and does not react with most other substances. Even at moderately high temperatures silica is chemically very stable. The reason for the low reactivity of silica is the very strong Si-O bond, but also its macromolecular structure.
Being the anhydrite of an acid itself (orthosilicic acid, H4SiO4), quartz will in general not be attacked by acids. The prominent exception is hydrofluoric acid, HF, which will decompose quartz to form first silicon fluoride SiF4, then hydrofluorosilicic acid, H2SiF6.
SiO2 is also attacked by alkaline substances (like calcium hydroxide, Ca(OH)2 as you said and potassium hydroxide, KOH). But note that the speed of the reaction depends on the modification and crystal size: Crystalline quartz will dissolve only very slowly in hot watery alkaline solutions, while amorphous SiO2, will be readily dissolved at room temperatures. So, in concrete, there would be reaction between quartz and the alkaline compounds of the concrete, typically Ca(OH)2, if the proportion of amorphous or cryptocrystalline (very fine crystalline) quartz increases. It leads to the formation of silica gels in concrete and as you know the silica gel attracts water, swells and cracks the concrete within a few decades. Then, using quartz in concrete is desirable as long as it is chemically inert (or is at least less reactive than the material which is replaced).
Hope it helps.
Thanks a lot for links, but 2 of them don't work and couldn't find my answer.
Ali,
Quartz's absolute hardness is 100.
Quartz is chemically inert.
Dear Hamed
As far as i understood, quarts actually reacts with extra Ca(OH)2 due to cement reaction with water, so it is not absolutely inert
Dear Ali,
Quartz is nearly always inert when used as aggregate (not fine powder as cement replacement material) in concrete. It means that it will not react at normal conditions. less reactivity, more controllable situation in concrete. That is the reason make it desirable for concrete as well as its hardness.
At room temperature, SiO2 in all modifications is almost inert and does not react with most other substances. Even at moderately high temperatures silica is chemically very stable. The reason for the low reactivity of silica is the very strong Si-O bond, but also its macromolecular structure.
Being the anhydrite of an acid itself (orthosilicic acid, H4SiO4), quartz will in general not be attacked by acids. The prominent exception is hydrofluoric acid, HF, which will decompose quartz to form first silicon fluoride SiF4, then hydrofluorosilicic acid, H2SiF6.
SiO2 is also attacked by alkaline substances (like calcium hydroxide, Ca(OH)2 as you said and potassium hydroxide, KOH). But note that the speed of the reaction depends on the modification and crystal size: Crystalline quartz will dissolve only very slowly in hot watery alkaline solutions, while amorphous SiO2, will be readily dissolved at room temperatures. So, in concrete, there would be reaction between quartz and the alkaline compounds of the concrete, typically Ca(OH)2, if the proportion of amorphous or cryptocrystalline (very fine crystalline) quartz increases. It leads to the formation of silica gels in concrete and as you know the silica gel attracts water, swells and cracks the concrete within a few decades. Then, using quartz in concrete is desirable as long as it is chemically inert (or is at least less reactive than the material which is replaced).
Hope it helps.
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