The Influence of Recycled Crushing Strength of RC Beams under Repeated Loading

This paper describes a study of the effect of crashed (recycle) concrete on reinforced concrete beams. Three-dimensionally nonlinear finite elements analysis has been used conducted the numerical investigations of the general study of recycling-beam. ANSYS.11.0 computer-program using in this paper. Solid65 using as element of concrete, link8 for steel. The compression strength of the concrete mix decrease due to the strength of crashing concert. It’s weaker than gravel aggregate, that lower strength due to weak of old mortar cement around the aggregate and due to crashed process. The percentage of decrease of the compressive strength equal to (59.8) % and deflection of beam increase due to weak of concrete and the load of initial crack, it’s lower than traditional concrete contains natural aggregate. Keywordscrushing concrete, repeated load, finite elements. How to cite this article: M.A.E. Al Hamdani, M.M. Hamid and N.M. Al Hussiny, “The Influence of Recycled Crushing Strength of RC Beams under Repeated Loading,” Engineering and Technology Journal, Vol. 37, Part C, No. 1, pp. 93-100, 2019.


Introduction
The need to develop economic and efficient methods to repair and recycle of concrete by crashing concrete and study the effect of repeated load on behavior beams composed by crashing concrete, that All results compared with finite element (Ansys program) final the paper found good agreement between them, but the comparison strength for crashing concrete weaker than the normal concrete with normal gravel due to replace crashing concrete with normal gravel because the crashing concrete weaker than normal gravel that will decrease the comparison strength of concrete and increase the deflection of beam. Table 1 and 2 shown chemical and Physical properties analysis of Ordinary Portland cement is used in this investigation and compared with Iraqi stander for Ordinary Portland cement type.

II. Sand
Fine natural sand from Al-Ekhaider was used; its grading is shown in Table 3, and Figure 1. Table 4 shows the specific gravity and sulfate content of fine sand, the latter being within the requirements of the Iraqi specification No. 45/1984. The sand was tested in the General Company for Geological Surveying and Mining.

Crashed (recycle) concrete
The crushed recycled concrete of maximum size 19mm was used in this investigation. The grading of crushed recycle concrete compared with Iraqi and ASTM C33 2002 stander, Table 5 shown that.

Compressive Strength
To select the mix proportion for the concrete used in preparing the reinforced concrete beams, three trial mixes were carried out to obtain cylinder strength of 30 MPa at 28 days by using the method of the design proposed by Nevile 2000. The final mix used was 1:1.42:2.41 by weight. The water-cement ratio was equal to 0.455 and cement content was 450 kg/m3, Table 6 shown that.

Specimens Description
Nine reinforced reactive powder concrete beams with rectangular cross-sectional dimensions of 150 mm width by 250 mm height and 2000 mm length were cast. The flexural reinforcement of the beams consisted of 2Ф12 mm tension bottom bars at the tension face and 2Ф12 mm top bars at the compression face. To avoid shear failure, the beams were over reinforced for shear with Ф10 mm closed stirrups spaced at 100 mm on center. Figure 2 shows specimen dimensions, reinforcement details, support locations, and location of loading points [4][5].

I. Steel Reinforcement
For all beams, two sizes of steel reinforcing deformed bars are used. Bar size Ф12 mm used as longitudinal reinforcement, and bars of size Ф10 mm were used as transverse reinforcement (closed stirrups). Table 7 shows the properties of steel reinforcement bars.

Finite Analysis
The finite element method is a numerical procedure, which can be applied to solve numerous engineering problems, that has become a powerful and versatile tool for structural analysis in both linear and nonlinear formulations of reinforced concrete structures. In the study, the finite element software ANSYS-Ver. 11 is used in the analysis. Some features of this program are discussed below [7].

I. Finite Element Idealization and Material Properties Concrete idealization
Three-dimensional brick element (Solid 65) is used to model the concrete with or without reinforcing bars (rebar). The element is capable of cracking in tension and crushing in compression.

II. Steel idealization
The steel reinforcing bars (tensile, compressive, and stirrups) are represented by using 2-node discrete representation (Link8 in ANSYS) and included within the properties of 8-node brick elements. Modeling of Reinforced Concrete Beam (Control Beam. The major factor in convergence study is the increase in mesh in x-direction. As a result, and to save time and efforts, it is thought that the number of elements, which is equal to 3, 4 and 40 elements in z, y and x-direction is sufficient to give good results. By taking advantage of symmetry for both geometry and loadings of beams, a half of the entire model beam was used for finite element analysis (i.e. the total number of elements for half of beam BNo.1 would be equal to 240 elements). Discrete representation was used to model all internal reinforcement. Figure 3 shows the picture of a meshed beam BNo.1 it was adopted for this study. The mesh shown in Figure 3 for beam BNo.1 is used for all tested beams (BNo.1 to BNo.9). While the representation of internal steel reinforcement for all tested beams (BNo.1 to BNo.9) are shown in Figure 9.

III. Loads and Boundary Conditions
To get a unique solution, the model should be constrained by using displacement boundary conditions. The displacement in Dx =0 (that 90 0 with the plane), but in the direction of load the displacement Dy≠0, the aim that, to the simulation of experimental conditions. The loading applied is repeated loa; Figure 5 shown the details of experimental conditions.

Figure 5: Details of boundary conditions and applied loads
The finite element model accurately predicts the failure load, cracks, moment and shear of the beam. The ANSYS program records the crack pattern at each applied repeated load step. Figure  6 shown the cracking load. On the other hand, the variations in stress and strain X-axis for beam are shown in Figure 6 and 7.

Results of Analysis Beams
On a show that legitimacy of the suggested numerical system for the dissection from claiming strengthened solid beams, the sum tried beams (BNo. 1 with BNo. 6) will be analyses by utilizing ANSYS workstation program, as specified formerly. The examination takes after the same system Likewise that provided for clinched alongside parts five What's more six taking under record the variety done material properties, measurements and other determinations depicted formerly paper. With incorporate the impact of strain solidifying to steel reinforcement, the stress-strain curve, following yielding for steel reinforcement, will bring incline equivalent to 2% from claiming that in front of yielding. 1. Load-deflection (under repeated load) Curves: The deflection was measured in the medal of the beam. Figure 9-17 show the deflection load curves ware plotted by finite elements compared with experimentally beam.

The Crack & Ultimate Loads
The cracking and Ultimate loads for the experimental and finite element results shown in Tale 8 and 9.

Conclusions
The Conclusions of this paper found the effect of add crashing concrete, found the compression strength of concrete mix decrease due to the strength of crashing concrete.It's weaker than gravel aggregate, that lower strength due to weak of old mortar cement around the aggregate and due to crashed process. The percentage of decrease of the compressive strength equal to (59.8) % and deflection of beam increase due to weak of concrete anda load of initial crack, it's lower than traditional concrete contains natural aggregate. From compariso, finite element result found the increment (average) results about 18% for all result, that good aggregate.