**3. Specimen preparation for capillary suction test**

sorption of cementitious composites. Reducing moisture content can, for example, lower thermal conductivity and reduce heat exchange through the materials in the building envelope. Water is mainly transported through the capillary pores in hcps. Since increasing water to cement ratio (w/c) increases capillary porosity, the first solution to reduce water permeability is usually reducing w/c [1]. Using pozzolanic materials such as silica fume, fly ash, and slag can also result in a denser pore structure and average pore size, which results in more resistance to water sorption. The other method to modify water permeability in cement-based materials is using hydrophobic agents. Both the material surface and the internal structure can be made water-repellant by using these agents [2–5]. While UV light of the sun can affect water repellence of the surface-treated material, internal hydrophobation does not have this drawback. In this chapter, water sorption of hcps as the important factor in permeability of cement-based materials is described. Moreover, the resistance number and the capillary number [6], which are calculated based on capillary suction test, will be described here. These numbers are used for the characterization of the material resistance to water sorption. However, this method is not suitable for modified structure of hcps that have high resistance to water sorption. Thus, an alternative parameter "effective moisture transport (*EMT*)" factor is proposed in this chap-

ter instead of the resistance number according to the experimental results.

below the water surface. The test is usually performed in the following order:

Smeplass and Skjølsvold [6] improved the test for capillary suction by including information about the pore structure of hardened concrete. Martys and Ferraris [7] have also studied capillary transport in mortars and concrete. In order to perform the capillary suction test, the specimens are usually placed in a ventilated incubator at 105°C until reaching constant weight. Lower temperatures (e.g., at 50°C in an oven or at 20°C in a desiccator) with longer drying interval may also be chosen to reduce the effect of drying on pore structure and composition of the material components. After drying, the specimens are placed on a grating 1–2 mm

The duration of each step may vary depending on the water resistance of the sample as well as its height. For ordinary materials, the standard test procedure in each country may be used; however, for modified materials, it may be necessary to adjust the test parameters such as

**2. Capillary suction test**

64 Cement Based Materials

**1.** drying to a constant weight, **2.** capillary suction for 4–5 days,

**5.** recording the specimen volume,

duration and water pressure.

**3.** submersion in water for 3–4 days at 1 atm,

**4.** submersion in water for 1–3 day at 50–80 atm,

**6.** drying the specimen at 105°C to reach a constant weight.

In case of concrete samples casted in the laboratory, 20-mm slices from cylinders cured for 28 days are usually cut for the test. To avoid material spalling from edges due to cutting, epoxy or other hard-wearing coating can be applied on the cylinders. **Figure 1** illustrates an example of sample preparation from concrete cylinders.

A similar procedure may be used for preparing hcp samples. The size of these specimens is usually smaller than concrete samples. The mixing procedure for hcps may also be different from ordinary concrete. Using a high-speed kitchen blender to facilitate proper mixing

**Figure 1.** Cutting specimens from concrete cylinders for capillary suction test [4].

of water and cement is popular in this process. The following order may be carried out for mixing: a 1-min medium rate mixing; cleaning the mixer wall with a flexible plastic spatula; a 4-min fast rate mixing; cleaning the mixer wall with a spatula and finally a 1-min slow rate mixing. Moreover, the admixtures (such as hydrophobic agents, plasticizer air-detraining admixture) may be mixed with water for 1 min, before adding to the cement to assure proper dispersion in the cement paste. The specimens with high w/c that have risk of separation may be cured on a slow-rate rolling machine on the first day.
