Evaluación de otros procesos cognitivos

4.10.1 General considerations

An additional set of sets was undertaken on behalf of Abbey Pynford to investigate the flexural and punching shear resistance of SFRC. Four sets of round panel tests were carried out as described below. All the plates were 125m thick with a diameter of 1m as described previously. The concrete mix details have been omitted at the request of Abbey Pynford.

 Cast 1 was a plain concrete mix. This mix was used as a benchmark with which the effect of the steel fibres could be assessed against.

 In Cast 2, Arcelor Mittal He-75-35 steel fibres were added at a dosage of 50kg/m3

. These are 35mm long hooked fibres with a 0.75mm diameter and an aspect ratio of 47. The tensile strength of the fibres was 1200MPa.

 Cast 3 incorporated Arcelor Mittal He-55-35 steel fibres at a dosage of 50kg/m3

. These are 35mm long hooked fibres with a 0.55mm diameter and an aspect ratio of 64. The tensile strength of the fibres was 1200MPa.

114  Cast 4 had Helix 5-25 fibres at a dosage of 50kg/m3

. These are 25mm long twisted wire fibres with a 0.5mm diameter and an aspect ratio of 50. The tensile strength of the fibres was 1700MPa.

One RDP and two punching shear tests were carried out for each concrete mix. The RDP was carried out to determine the flexural strength of the SFRC. The geometry adopted for this test is shown in Figure 4.33. The punching shear resistance was determined by testing round plate tests supported around their perimeter by a precast manhole ring. A polythene sheet was placed between the round plate and the manhole ring to reduce the effect of friction. A thin layer of mastic was injected between the polythene and the slab to ensure contact of the slab with the manhole ring.

The round plates were reinforced with either one or two B16 reinforcement hoops in the punching shear tests. The function of the reinforcement hoops was to increase the flexural capacity of the round plates sufficiently for punching failure to occur. The round plate was reinforced with a single B16 hoop of diameter 800mm in the Type I punching tests (Figure 4.34). Punching Test Type II was reinforced with two B16 hoops of diameters 800mm and 950mm (Figure 4.35). The hoops were placed in the bottom of the slabs with 25mm cover.

The measurement of the deflection was made by a Linear Variable Deflection Transducer (LVDT) incorporated within the actuator. The slab was loaded at a controlled rate of displacement of 0.5/min.

115

Figure 4.34: Depiction of punching test type 1, with a single B16 hoop

116

Figure 4.36: Loading arrangement of punching shear tests

4.11 Concluding Remarks

This chapter provides a brief overview of the experimental methodology adopted in this research. The concrete mix design was described along with each of its constituents. This was followed by a brief overview of the standard three-point bending beam test (BS EN 14651:2005) which was used to determine the flexural strength of the SFRC.

A novel round plate test was described. The thickness of the slab was chosen to be the same as the depth above the notch in the BS EN 14651 notched beam. This test has some similarities with the ASTM C-1550 round panel test. A novel upside down round plate test is described in which the slab is loaded from its bottom surface to enable crack widths to be measured during the test. The aim of the tests is to relate the crack width to the central displacement of the plate.

The two-span one way spanning slab tests are intended to simulate a pile supported slab failing in a wide beam mode. The effect of axial restraint was measured in one of the tests. Careful measurements were taken of crack widths and slab displacements to enable the two to be related. Additional round plate tests were undertaken in order to investigate the effect if fibres on punching shear resistance. The results of the experiments described herein are described in Chapter Five.

117

Chapter Five

Experimental Results

5.1 General Remarks

This chapter presents the results of the experiments, described in Chapter Four. The results are presented in the same sequence as the tests are described in Chapter Four. The failure mechanisms are described with emphasis on the crack pattern as well as the crack widths. The results presented in this chapter form the basis of the analytical and numerical works described in Chapter Seven.

5.2 Control Specimens

5.2.1 General Overview

As described in Chapter Four, a total of 24 control specimens – 12 cubes and 12 cylinders – were cast alongside each batch of specimens. Half of these were cured in water for 28 days, whereas the remaining specimens were cured under polythene and wet hessian.

5.2.2 Compressive Test

Table 5.1 summarises the cube strengths for casts C1 to C4. The cubes measured 100 mm x 100mm x 100mm.

Cast Under polythene (MPa) Standard Deviation (MPa) In water (MPa) Standard Deviation (MPa) C1 48.6 3.94 49.5 1.25 C2 54.8 2.66 52.5 2.57 C3 41.4 1.40 41.7 3.51 C4 45.1 1.64 48.0 1.6

118 5.2.3 Splitting ‘Brazilian’ Test

The concrete tensile ‘splitting’ strength was measured using the ‘Brazilian’ test on cylinders with a diameter of 100mm and height of 254mm. The tensile strength was evaluated using the following expression (Neville, 1995):

DB F

t

_



where, Fdenotes the failure load of the specimen, DandBdenote the diameter and height of the specimen, respectively. The results of the Brazilian tests are summarised in Table 5.2 below:

Cast Cured under polythene (MPa) Standard Deviation (MPa) Cured in water (MPa) Standard Deviation (MPa) C1 4.0 0.78 4.4 0.47 C2 4.5 0.21 4.2 0.34 C3 4.6 0.35 4.8 0.57 C4 4.3 0.47 3.9 0.50

Table 5.2: Average concrete tensile strength