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Concrete sealers are applied to concrete to protect it from surface damage, corrosion, and staining. They either block the pores in the concrete to reduce absorption of water and salts or form an impermeable layer which prevents such materials from passing.
Silica fume is an ultrafine material with spherical particles less than 1 μm in diameter, the average being about 0.15 μm. This makes it approximately 100 times smaller than the average cement particle. [4] The bulk density of silica fume depends on the degree of densification in the silo and varies from 130 (undensified) to 600 kg/m 3. The ...
Fumed silica with surface area of 130 m 2 /g . Fumed silica (CAS number 7631-86-9, also 112945-52-5), also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles.
The pozzolanic reaction, which is specific to siliceous and/or aluminous additions (fly ash, blast-furnace slag, silica fume, calcined clay, etc.) in composite cement, can strengthen the continuous hydration of cement grains in terms of long-term CSH development and, as a result, a certain degree of autogenous self-healing.
Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface-to-volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability. [63]
However, silica fume has to be very finely dispersed in the concrete mix because agglomerated flakes of compacted silica fume can themselves also induce ASR if the dispersion process is insufficient. This can be the case in laboratory studies [citation needed] made on cement pastes alone in the absence of aggregates. Silica fume is sufficiently ...