ACI CCS-4(20) Concrete Craftsman Series Shotcrete For The Craftsman.
little cementitious action when used alone, but when used with portland cement, they react with products of cement hydration to develop additional cementing action. Some of the finely divided minerals have both cementitious and pozolanic properties.
The most commonly used pozzolans in shotcrete are silica fume and fly ash. Undensified silica fume, sometimes called microsilica. is a pozzolan with particles only one hundredth the size of cement particles. Silica fume is a very fine noncrystalline silica produced in electric arc furnaces as a byproduct of the production of elemental silicon or alloys containing silicon.
Fly ash is a finely divided residue that results from burning groLmd or powdered coal as in coal-burning power plants. Fly ash particles arc spheres with a diameter similar to that of portland cement particles. In addition to improving hardened properties of concrete. silica fume and fly ash are commonly used to improve the plastic properties of the fresh shotcrete.
Most poii.olans reduce the permeability of concrete by filling in the spaces between cement particles, thus improving durability. In the amounts normally used, some pozzolans cause a reduction of early strengths up to 28 days hut improve the long-term strength. Because some pozzolans react slowly, longer curing and protection of the surface from freezing or contact with aggressive substances are often recommended for concrete containing pozzolans.
The sand, gravel and crushed stone that are mixed with cement and water to make concrete are called aggregates. Aggregates make up 70 to 80 percent of concrete by weight. A cubic yard (yd3) of normal weight concrete may contain 2800 to 3200 lb of aggregates (a cubic meter [m3J of normal weight concrete may contain 1600 to 1 800 kg of aggregates). This distribution is shown in Fig. 2.l.2b.
Concrete that is made without coarse aggregate is usually called mortar or grout. Most concrete used in building construction has a maximum aggregate size from 3/8 to 1-1/2 in. (10 to 40 mm). In massive concrete structures like darns and mat foundations, large aggregate sizes of 6 in. (150 mm) or more are often used.ACI CCS-4 pdf download.