Test Methods

3.6.1. Mechanical Tests

Compressive tests were conducted on some of the mixtures. These tests were made on 100 mm or 150 mm cubes. The loading rate was constant and same for all concretes. Strength tests of mortars, however, were done in accordance with the RILEM-Cembureau Method. The beams prepared for the standard RILEM- Cembureau tests were 160 mm in length and 40 mm x 40 mm in cross-section. After the bending tests, the compressive tests were performed on the half beams using 40 mm x 40 mm cross-section.

Splitting strengths of some mixtures were determined. Six cylinders of 150 mm diameter and 60 mm height were used for the splitting tests.

Modulus of elasticity tests were made on cylinders of ø100x200 mm or ø150x300 mm. The elastic moduli were calculated from the stress-strain curve for stresses below approximately 30 percent of the ultimate strength.

In order to obtain the complete stress – strain curve of the slag concretes presented in Chapter 3.3.2.1, these concretes were tested in uniaxial compression in a close-loop test machine. 100x200 mm cylinders were used and both ends of the specimens were ground before testing in order to obtain smooth surfaces.

The Brittleness Index B, obtained from the loading-unloading curve, is defined as the ratio of the elastic deformation energy to the irreversible deformation energy corresponding to the pre-peak point of the stress-strain curve. As shown in Figure 3.2, Brittleness Index B may be expressed as the ratio of area SII to area SI, where SI is the irreversible deformation energy due to damage and SII is the elastic (reversible) deformation energy. When the ratio of SII/SI approaches zero, all energies become

Rock cylinder (Model aggregate) Cement paste 150 mm 60 mm

irreversible; when it tends to infinity, all energies become reversible. Thus, an increase in B indicates increased brittleness (Brandt, 1995).

Figure 3.2: Reversible and irreversible energies 3.6.2. Capillary Water Absorption

Capillary water absorption test was made according to Norwegian test method NT 368 (1991). Six concrete discs of 100 mm diameter and 25 mm height were used in the test. Specimens were first dried at 105oC to constant weight and preconditioned before exposure to water absorption. The specimens were exposed to one side and the changes in weights were recorded for four days. The rate of water absorptions were estimated based on the weight gain, and the square root of time vs. the capillarity water absorption graphs were obtained. A schematic time – water suction graphic is given in Figure 3.3.

Linear lines are fitted to the test data by regression analysis as shown in Figure 3.3. The intersection of these two lines represents the time (tcap) when the capillary pores are filled and the waterfront reaches the top. The capillary number (k) is the slope of the line in the first stage of water absorption and calculated as follows:

cap cap Q k t = (3.1)

where Qcap is the amount of water absorbed in a period of time tcap after which a distinct change in the rate of water absorption occurs.

Deformation

Figure 3.3: Schematic representation of water suction by time

A capillary resistance number (m) describes the relative time that the water front reaches the top of the specimen and is given by:

2 cap t m l = (3.2)

where l is the thickness of the specimen. 3.6.3. Porosity

The specimens used for the capillary water absorption test are also used for the calculation of the concrete porosity. After the capillarity test, the specimens are immersed into water for 3 days to ensure complete saturation. Then the specimens are further saturated under a pressure of 5 MPa. After the pressure saturation, the weight of the specimen in water is measured. Finally, the dry weight is obtained after drying at 105oC. The following porosity parameters can then be calculated:

Total porosity: 3 1 3 4 100 tot W W x W W ε = − − (3.3) Suction porosity: 2 1 3 4 100 suc W W _x W W ε = − − (3.4) Air porosity: 3 2 3 4 100 tot W W x W W ε = − − (3.5)

Frost protection number: air tot PF ε ε = (3.6) tcap Qcap

Square root of time

where; W1 = weight of oven dry specimen

W2 = weight of specimen after three days immersion in water W3 = weight of specimen after pressure saturation

W4 = weight of specimen in water after pressure saturation 3.6.4. Test Methods for Evaluating Chloride Penetration

ASTM C1202, NT 492 and NT 433 test methods were used in this study for the evaluation of resistance of concrete to chloride penetration.

ASTM C1202 (1997) Rapid Chloride Permeability Test is based on the electrical conductivity of the concrete. Concrete discs of 100 mm in diameter and 50 mm in height were used for the test. The curved surface of the specimen is coated with epoxy first. Before the test, a standardized vacuum saturation procedure was applied to the specimens. Specimens were put between test cells, one of which containing NaCl solution and the other NaOH solution. The concrete sample was then subjected to a potential difference of 60 V and the total charge passing through during the first 6 hours was measured and expressed in terms of Coulombs as a basis for the evaluation of the concrete chloride permeability.

NT 492 (1999) is based on a non-steady state migration of chloride ions into the specimen. Same type of specimens and same vacuum treatment for ASTM C1202 test are used for the test. After preconditioning, the samples were assembled in a water sleeve and tightened with steel clamps. The specimens were then placed in a container filled with NaCl solution. The rooms of the sleeve above the specimens were filled with a solution of NaOH. An external potential was then applied axially across the specimen to force chloride ions migrate into the specimen. The level of potential depends on the concrete quality. At the end of a certain test duration, the specimens were axially split into two pieces and silver nitrate solution was sprayed onto the fresh split surface. The chloride penetration depth was then measured from the visible white silver chloride precipitation. By using this depth, the chloride migration coefficient was calculated based on the Nerst-Planck equation.

NT 443 (1995) test, also called “bulk diffusion test”, is based on the immersion of sample into a chloride solution. A concrete cylinder was epoxy coated first and then cut into half perpendicular to the axis of the cylinder for leaving a surface for exposure to the salt solution. The specimen was then immersed in a solution of 3 N

NaCl. After a certain period of exposure, powder samples were obtained at every 1 mm depth by grinding off concrete in parallel to exposed surface. The profile of the chloride penetration was then determined by chemical analysis on the powder samples. A spectrophotometric method was used for the determination of the chloride content. Based on the chloride profile obtained, the effective chloride diffusion coefficient was calculated according to Fick’s law of diffusion.

3.6.5. Test Methods for Measuring Electrical Resistivity

Two type of resistivity measurements were performed on some of the concrete mixtures; two electrode method and wenner electrode method.

The test setup for the two electrode method is shown in schematically in Figure 3.4. A resistance meter with an alternating current at the frequency of 1 kHz was used. The resistivity of concrete was calculated as follows:

concrete measured

A R

L

ρ = (3.7)

where ρconcrete : resistivity of concrete, Rmeasured : resistance of concrete, A : surface area of concrete, L : length of the specimen.

Figure 3.4: Resistivity testing of a concrete using two external electrodes

Four point wenner technique was also used for measuring the resistivity of concrete. Schematic representation of wenner electrode method and the flow lines are shown in Figure 3.5. CNS Farnell RM MKII wenner electrode was used for the tests. Probe spacing of 25 mm was chosen for the cubes and ø100x50 mm disc specimens and 50 mm spacing for the cylinders. Specimens were tested in saturated – surface dry condition. The wenner electrode used has wooden probe tips and the tips were in

R