**2. Experimental program**

### **2.1 Materials used and concrete mix design**

There is no single branded procedure available for mix proportion for HSC, therefore careful selection of the materials is also effective in production of HSC [4]. The ACI 318 [5] defines HSC as concrete with a compressive strength >41 MPa.

The concrete used to prepare the HSC beams is made from the following constituents:

**Cement**: cement used in this work was an Ordinary Portland Cement of type CEM I 52.5 N CE CP2 NF, and was provided by Lafarge group (cement of St-Pierre-la-Cour of Laval in France). The density of this cement is 3160 kg/m<sup>3</sup> and its specific surface is 3520 cm2 /g, therefore falling within the range of cements that can formulate a HSC (between 3500 and 4000 cm<sup>2</sup> /g) [6]. The particle sizes vary between 0 and 100 μm.

**Fine aggregate**: the sand used to make a HSC must have a modulus of fineness greater than or equal to 2.8. The Sand with a modulus of fineness <2.5 makes the concrete sticky and therefore difficult to compact and less resistant [7]. Rolled sand from the Loire region in France, is used for the present work, with a granular class of 0/4 (mm). The fineness modulus of this sand was measured at a value between 2.9 and 3.1. This sand also has a water demand of <0.5% of its mass.

**Coarse aggregate**: to make the HSC, the ideal granulate must be crushed, cleaned, of regular shape, with a reduced angularity, and containing less flat particles or elongated [8, 9]. Crushed gravel from quartz, with a granular class of 4/15

*Experimental and Theoretical Investigation on the Shear Behaviour of High Strength Reinforced… DOI: http://dx.doi.org/10.5772/intechopen.86499*

(mm) is used for the present work. This gravel has a water demand of the order of 2–3% of its mass.

**Fine mineral additions**: fine mineral additions consisting of blast furnace slag and limestone fillers. The slag additives were finely ground to give a specific surface of 7000 cm2 /g and were used in proportion of 10% by weight of cement. This type of addition was provided by Ecocem in France. The fine limestone fillers is Betocarb®HP-EB, manufactured by the Omya-Meac Group in France, and were used in proportion of 23% by weight of cement. The mineral additives were used to fill in the finer gaps between the aggregates and hence to improve the density and the compactness of the concrete material.

**Superplasticizer**: a high range water reducing admixture (HRWRA) in a liquid form, based on polycarboxylates (CHRYSO Fluid Optima 206), was used in a proportion of 2.5% by weight of cement. It is interesting to add the superplasticizer in 1/3 of the quantity with the mixing water to ensure the dispersion of the cement grains, and 2/3 remaining at the end of mixing [10].

**Water**: potable tap water is used.

material, and there is a lack of base data for shear strength of HSC beams, so all the models proposed by the design codes and developed essentially for normal strength concrete (NSC) were extrapolated to HSC, to validate the applicability of these empirical methods to this material. More investigation work is then required to

The present chapter aims to improve the structural behaviour of HSC beams particularly the shear, and thus ameliorate the performance of the built environ-

The HSC presents a low resistance under shear [1–3] because the crack surfaces are smooth and cross the aggregates particles as shown in **Figure 1**, which shows a low contribution of the aggregates in the shear strength. However, the HSC is characterised by high compressive strength and by better adhesion with steel reinforcement, which gives a best contributions of the compression zone and the dowel

There is no single branded procedure available for mix proportion for HSC, therefore careful selection of the materials is also effective in production of HSC [4]. The ACI 318 [5] defines HSC as concrete with a compressive strength >41 MPa. The concrete used to prepare the HSC beams is made from the following

**Cement**: cement used in this work was an Ordinary Portland Cement of type CEM I 52.5 N CE CP2 NF, and was provided by Lafarge group (cement of St-Pierre-la-Cour of Laval in France). The density of this cement is 3160 kg/m<sup>3</sup> and its

**Fine aggregate**: the sand used to make a HSC must have a modulus of fineness greater than or equal to 2.8. The Sand with a modulus of fineness <2.5 makes the concrete sticky and therefore difficult to compact and less resistant [7]. Rolled sand from the Loire region in France, is used for the present work, with a granular class of 0/4 (mm). The fineness modulus of this sand was measured at a value between

**Coarse aggregate**: to make the HSC, the ideal granulate must be crushed, cleaned, of regular shape, with a reduced angularity, and containing less flat particles or elongated [8, 9]. Crushed gravel from quartz, with a granular class of 4/15

2.9 and 3.1. This sand also has a water demand of <0.5% of its mass.

/g, therefore falling within the range of cements that can

/g) [6]. The particle sizes vary

cover this aspect and provide further information.

*Diagonal cracking crossing the aggregates in HSC.*

action effect to the shear strength of HSC beams.

**2.1 Materials used and concrete mix design**

formulate a HSC (between 3500 and 4000 cm<sup>2</sup>

**2. Experimental program**

specific surface is 3520 cm2

between 0 and 100 μm.

constituents:

**46**

**Figure 1.**

*Digital Imaging*

ment to ensure an adequate durability of constructions.

The mix designs used in making the HSC beams are presented in **Table 1**.

#### **2.2 Mechanical properties of concrete**

The compressive strengths of HSC used in making the beams without transverse reinforcement and with transverse reinforcement were measured through the crushing tests of cylindrical concrete specimens of 80 mm diameter by 160 mm in height, using a press with capacity of 500 kN. Measurements of the longitudinal compressive strains were carried out with the help of an extensometer (**Figure 2**) and enabled the modulus of elasticity of the HSC. The results were recorded in a data acquisition system (**Figure 3**) for the complete stress-strain curve of HSC (**Figure 4**).

The tensile strength was also evaluated for the HSC by splitting tests of concrete cylinders, 80 mm in diameter and 160 mm in height.

**Figure 4** shows that the pre-peak behaviour is quasi-linear with greater rigidity, and the average ultimate deformation (*εcu* = 2%) decreases with the increase in the compressive strength, which is below the ultimate deformation required by the different universal design codes (*εcu* = 3.5%) which reflects a decrease in ductility. It should be noted that the HSC specimens exhibit brittle and explosive fracture resulting from a lack of ductility, major disadvantage of this material, as shown in **Figure 2**.

The results of the compressive strength *fc*, the tensile strength *ft* and the modulus of elasticity *Ec* of HSC are shown in **Table 2**.

#### **2.3 Steel reinforcement**

The longitudinal reinforcement composed of two high yield bars of 10 mm diameters in the top zone of the beam (compression), two high yield bars of 8 mm diameters in the bottom zone of the beam (tension) and 6 mm for the transverse reinforcement in the form of stirrups, as shown in **Figures 6(a)** and **7**. The steel was


**Table 1.** *Mixing ingredients of HSC (kg/m<sup>3</sup> ).*

**Figure 2.** *Concrete cylinder compression test.*

To find a precision in the experimental results, three beams were tested in each

The beams were tested under monotonic static loading using a 250 kN servocontrolled hydraulic jack (**Figure 8**). The details of the beams tested are presented in **Table 3**. It is noted that the value of shear-span/effective depth ratio (a/d) is within the a/d ranges leading to a dominant shear behaviour which results in a shear

*Direct tensile test and measurement of the steel deformations by Gom-Aramis software (using DIC).*

*fc* **(MPa)** *Ec* **(GPa)** *ft* **(MPa)** 65 (3) 45.2 (5) 6 (1)

*Experimental and Theoretical Investigation on the Shear Behaviour of High Strength Reinforced…*

failure of the reinforced concrete beams [6, 12–16].

series.

**Figure 5.**

**49**

**Table 2.**

**Figure 4.**

*Stress-strain curve in compression of HSC.*

*DOI: http://dx.doi.org/10.5772/intechopen.86499*

*Average mechanical properties of HSC.*

**Figure 3.** *Data acquisition system for the compression test.*

tested under direct tension using a machine with capacity of 500 kN to determine the Young's modulus and the elastic limit. Measurement of the current deformations is carried out by Gom-Aramis software [11] using Digital Image Correlation (DIC) technique (**Figure 5**). The test results give a Young's modulus of 204 GPa and an elastic limit of 500 MPa.
