Compressive strength, psi, range Modulus of rupture, psi, range Shear strength, psi, range Tensile strength, psi, range Elastic modulus, psi, range Toughness Range Avg Wear resistance Range Avg Granite 7,70060,000 1,4305,190 2,0004,800 6001,000 5,700,0008,200,000 827 13 43.987.9 60.8 Marble 8,00050,000 6004,900 1,3006,500 1502,300 7,200,00014,500,000 223 6 6.741.7 18.9 Limestone 2,60028,000 5002,000 8004,580 280890 1,500,00012,400,000 520 7 1.324.1 8.4 Sandstone 5,00020,000 7002,300 3003,000 280500 1,900,0007,700,000 235 10 1.629.0 13.3 Quartzite 16,00045,000 530 15 Serpentine 11,00028,000 1,30011,000 8001,600 4,800,0009,600,000 13.3111.4 46.9 Basalt 28,00067,000 638 23 Diorite 16,00035,000 638 23 Syenite 14,00028,000 Slate 6,00015,000 2,0003,600 3,0004,300 9,800,00018,000,000 1056 5.611.7 7.7 Diabase 650 19 Building limestone 38 4.4 TABLE 4.12 Permeability of Commercial Building Stones [in3 / ( ft2)(hr) for 1/2-in thickness] Pressure, psi 1.2 50 100 Granite 0.060.08 0.11 0.28 Slate 0.0060.008 0.080.11 0.11 Marble 0.060.35 1.316.8 0.928.0 Limestone 0.362.24 4.244.8 9.0109 Sandstone 4.2174.0 51.2 221 TABLE 4.11 Specific Gravity and Porosity of Commercial Building Stones

Powered internal vibrators are usually used to achieve consolidation. For thin slabs, however, high-quality, low-slump concrete can be effectively consolidated, without excess water, by mechanical surface vibrators. For precast elements in rigid, watertight forms, external vibration (of the form itself) is highly effective. External vibration is also effective with in-place forms, but should not be used unless the formwork is specially designed for the temporary increase in internal pressures to full fluid head plus the impact of the vibrator (Guide to Formwork for Concrete, Except in certain paving operations, vibration of the reinforcement should be avoided. Although it is effective, the necessary control to prevent overvibration is difficult. Also, when concrete is placed in several lifts of layers, vibration of vertical rebars passing into partly set concrete below may be harmful. Note, however, that revibration of concrete before the final set, under controlled conditions, can improve concrete strength markedly and reduce surface voids (bugholes). This technique is too difficult to control for general use on field-cast vertical elements, but it is very effective in finishing slabs with powered vibrating equipment. Manual spading is most efficient for removal of entrapped air at form surfaces. This method is particularly effective where smooth impermeable form material is used and the surface is upward sloping. On the usual building project, different conditions of placement are usually encountered that make it desirable to provide for various combinations of the techniques described. One precaution generally applicable is that the vibrators not be used to move the concrete laterally. (Guide for Consolidation of Concrete, ACI 309R.) The interior of columns is usually congested; it contains a large volume of reinforcing steel compared with the volume of concrete, and has a large height com- pared with its cross-sectional dimensions. Therefore, though columns should be continuously cast, the concrete should be placed in 2- to 4-ft-deep increments and consolidated with internal vibrators. These should be lifted after each increment has been vibrated. If delay occurs in concrete supply before a column has been completed, every effort should be made to avoid a cold joint. When the remainder of the column is cast, the first increment should be small, and should be vibrated to penetrate the previous portion slightly. In all columns and reinforced narrow walls, concrete placing should begin with 2 to 4 in of grout. Otherwise, loose stone will collect at the bottom, resulting in the formation of honeycomb. This grout should be proportioned for about the same slump as the concrete or slightly more, but at the same or lower water-cementitious material ratio. (Some engineers prefer to start vertical placement with a mix having the same proportions of water, cement, and fine aggregate, but with one-half the quantity of coarse aggregate, as in the design mix, and to place a starting layer 6

Plasticiser Dry silo mixer A major piece of equipment that contains all the dry materials to produce mortar mixed on demand Take care around the moving parts of drum mixers! They are powerful machines and need to be treated with respect. Dry silo mixer Drum mixer Ready mix arriving on a site An operative mixing by hand There will still be occasions when there will be a need to mix mortar by hand for smaller jobs. For example, a small garden wall may be difficult to access with machinery such as a mixer, so mixing by hand will be the only option. Whatever method is used to mix mortar, always keep in mind the hazards associated with the materials used. These are covered in more detail in Chapter 1, but when preparing and placing mixing materials prior to building brickwork, remember that cement and lime powders can irritate your skin and aggregates Research the health effects of irritation are heavy to move especially when wet. from cement and lime dust. Find out what diseases can be caused.