*4.1.5 Strength of the cement*

Tests measuring the rate at which a cement can develop strength are usually carried out on mortar or concrete. There are numerous factors affecting strength, such as cement–fine aggregate ratio, water–cement ratio, the manner of mixing and molding, size and shape of a specimen, curing conditions, and age and loading conditions.

Before testing strength, it is important to note that cement strengthens over time; thus, a strength test should be performed at a specific time. Most cement strength tests are conducted at 3, 7, and 28 days. However, a one-day strength test may be performed for rapid hardening cement types.

• Compressive strength

In a test to determine compressive strength, a cylinder- or cube-shaped test specimen is subjected to a continuous compressive load under a hydraulic presser until failure. The loading sequence should be between 20 seconds and 80 seconds [21].

• Flexural strength

Flexural strength is a measurement of tensile strength in bending. The test is performed on a 40 x 40 x 160 mm rectangular concrete or mortar, which is subjected to a load at its center point until failure, according to ASTM [22].

#### *4.1.6 Hydration heat of the cement*

Hydration of cement generates heat, which can affect the cement's quality. When the heat generated is high, it may cause undesired stress, especially in large structures. The heat of hydration is affected mostly by the presence of tricalcium aluminate (C3A) and tricalcium silicate (C3S) in cement, in addition to fineness of the cement, water–cement ratio, and curing temperature. The heat of hydration of cement can be calculated according to ASTM [23]. This test method provides the apparatus and procedure for using isothermal conduction calorimetry to determine the total heat of hydration of cementitious materials at test ages up to 7 days.

*Characterizations of Cement and Modern Sustainable Concrete Incorporating Different Waste… DOI: http://dx.doi.org/10.5772/intechopen.100447*
