Behavior of Recycled Aggregate Fibrous Reinforced Beams Under Flexural and Shear Loading

The use of recycled concrete aggregates (RCA) to replace part or all of the natural coarse aggregates (NCA) in the production of concrete has been on the increase. Such use helps in the protection of the natural resources and in the reduction in the use of landfills. The experimental work consists of casting and testing ten rectangular simply supported reinforced concrete beams of dimensions (1500*150*240) mm with concentric point load at mid span as well as tests for control specimens to determine the mechanical properties of the concert. Five beams of these ten beams were designed to fail in flexure and other five beams were designed to fail in shear. Two beams were considering as a reference beams using normal aggregate (NCA) and two beams were considering as a reference beams using recycled aggregate (RCA. The other six beams were cast using recycled concrete aggregates (RCA) with steel fiber in three different volumetric ratio (vf).The present investigation contains three main variables: Coarse aggregate (normal and recycled). Transverse reinforcement (with stirrups spacing 50 mm for flexure failure mode and without stirrups for shear failure mode). Steel fiber (vf) = (0.5) %, (1) % and (1.5) %. In addition, constant longitudinal reinforcement ratio 0.012 . Experimental results have generally showed that ultimate loads (Pu) of beams made with RA are approximately close to the results of beams made with NA but with decrease of values (14% and 21%) for flexural and shear behavior respectively. The ultimate load of fibrous concrete beams is greater than beams without steel fiber by (33% -50%) for shear behavior and (21% -35%) for flexure behavior. KeywordsNormal aggregate concrete (NAC), Recycled aggregate concrete (RAC), Normal coarse aggregate (NCA) Recycled coarse aggregate (RCA), volumetric ratios of steel fiber (vf). How to cite this article: E.K. Sayhood, A.S. Resheq and F.L. Raoof, “Behavior of Recycled Aggregate Fibrous Reinforced Beams Under Flexural and Shear Loading,” Engineering and Technology Journal, Vol. 37, Part C, No. 3, pp. 338-344, 2019.


Introduction
Concrete is the single most widely used material in the world. In all construction of buildings work such as infrastructures, defense, low and high buildings, and sustainability of the construction industry [1]. At present, the concrete industry consumes almost12 billion tons of natural aggregates yearly. Such a large consumption can cause extensive destruction of the environment. Utilization of recycled aggregates can reduce the environmental impact and preserve the natural resources used in concrete applications [2]. Reuse demolition waste is one of the primary objectives of sustainable construction. In summary, the benefits of using round aggregates are as follows:

I. Environmental Significance
Recently, the interest of the environmental impacts of construction and sustainable development, recycled concrete is an effective resource to compensate for the exhaustion of natural resources. It is an inactive substance, making it an ideal way to recycle building debris. They are energy-efficient, continue to gain strength over time, and can be recycled old reinforced concrete and used as aggregates in new concrete.

II. Economic Factors
Concrete recycling is an attractive option for government agencies and contractors alike. Most municipalities impose strict environmental controls on opening new-pooled sources. In many areas, the cost of starting new quarries is increased. For demolition contractors, the area of landfills is limited and can be remote, especially in urban areas. Thus, disposal of old concrete and construction is costly. Dump charges are also likely to increase as construction debris increases and fewer landfill sites become accessible. Moreover, the cost and transportation distances of traditional aggregates can continue to increase with the scarcity of resources.

III. Save Energy
According to the Kajima Institute for Technical Research (2002), Kajima is developing a method to recycle the crushed concrete used in construction, known as the on-site recycling system. Recycling, manufacturing, and use are carried out at the same location. This can provide energy to transport materials to recycling plants.
Although there are many advantages to using recycled aggregates. However, there are still some defects [3] like: 1) High absorption of water.
3) Drop in strength. It is generally realized that there is a critical potential purpose behind decimated flotsam and debris reusing, to utilize in esteem added utilizations to get the most out of cost-effective and natural benefits. Because of that, reusing designing in many country around the world, convert low-esteem wastes into subordinate materials, for example, a fluctuation of total fines (dust), total levels, and street materials, and these materials are regularly utilized in the street make, second rate creation of cement, refill for holding dividers, brickwork, seepage, and square work for minimal effort outline [4]. Asian nations ought to truly consider RCA applications because of the developing of solid release for consistently [5]. Hong Kong, Japan, and China have transformed into pioneer areas in Asia, which effectively coordinated investigations on RCA asks for in building industry [6]. The crushers, which are utilized as of late for the reusing of rubble, were not planned or grown particularly for a reason. The greater part of crushers began from coal and preparing from regular stone pulverizing plants. Crushers were changed to adjust the level of size decrease, and the molecule estimate appropriation. A cone crusher and jaw crusher and Impact crusher *Jaw crusher included of two plants settled at one plate, stays fix while the other plate wavers forward and backward with respect to the settled plate. *Impact crusher: utilize overwhelming steel blow bars" mounted on an even or vertical rotor to more than once affect solid sections and heave them against steel iron blocks or "break plates" in the crusher lodging. The rotor keeps on tossing particles that are bigger than the coveted best estimate. The major objective of present work that investigated the flexural and shear behavior of reinforced concrete beams that use recycled aggregates (RA) from waste concrete as a full replacement for natural aggregates (NA) with the maximum size (19 mm) and with an addition of steel fibers in three different percentage.

Materials Used and Mix Design
In this work, the materials used for casting concrete beams are : In this study, the workability of concrete is reduced for two main reasons: First, the needle shape of the steel fiber affects the internal structure of the concrete, where the new concrete becomes stiffer and resistant in fresh condition. The second reason is the rough surface and the angular shape of the recycled aggregate. Therefore, superplasticizers were used to control the workability for all mixes except the control one.

Experimental Work
Ten concrete beams of dimension (1500*150*240) were tested in this work under increment load up to failure, moreover, to recording the deflection at mid-span, cracking load and maximum load. Five of them were designed to fail in flexure in Figure (2-a), the other beams were designed to fail in shear (without stirrups), Figure  (2-b). The ten beams were divided into four groups, as shown in Table 2.

I. Compressive quality
The compressive strength of concrete is the most common measure for judging not only the ability of the concrete to withstand the load, but also the quality of the hardened concrete in structural design. This results obtained from compressive strength, the test was performed by ASTM C 39/C 39M-03 (

II.Splitting tensile strength (ft)
It is one of the important property of concrete in a hardened stage which that indicated to cracking of the concrete, often refers to tension stress, the test was performed according to ASTM C496/C496M-11.

IV. Modulus of Elasticity (Ec)
Elastic modulus one of the important property of concrete. It was determined according to the ASTM C469-02.It can be obtained by carrying a compressive test on concrete cylinders Table 6 and Figure 6 illustrate values of elastic modulus for various strength and the predicted values using the following equations: (ACI 318M-2014), Ec = 4700√ ′ (4)  The values of cracking load for the control beam with natural aggregate greater than the value of control beam with recycled aggregate when the other parameters are kept fixed. It was already interactive and exposed to tensile stress thus the bonding with the remain concrete component would be little then the cracking load (Pcr) would be lower. But when steel fiber with different percentage (0.5, 1 and 1.5%) was added, observed improvement of concrete in cracking load. Percentage of these increments is about (60.7-94) % for flexural behavior and (66-166) % for shear behavior. For the same reason , the decrease in the ultimate load due to the addition of recycled aggregate will be compensated when the Steel fiber in different percentage was added by increase about (21-35)% for flexural behavior and about (33-100)% for shear behavior.

VI. Load Deflection Behavior
Deflection in this work was measured at mid-span of all tested beams. Table 8 shows the maximum deflections of the beam with the ultimate load. Fig.7 shows the load-deflection curves of all beams; and Fig.8 shows failure mode and Crack patterns for some tested beams.   Ten rectangular beam specimens were tested to assess the effects of replacing all the natural aggregates with recycled aggregates in addition to conformable 15 cubes, 45 cylinders, and 15 prisms specimens, results were explained as below: 1) Test results of mechanical properties of normal concrete replace with RA mixes decrease than NA mixes by (20%, 17%, 18%, and 9%) respectively 2) The effect of 0.5% steel fibers on mechanical properties of concrete gives larger values than the non-fibrous concrete by (18%, 24%, 24%, and 14%).
3) The effect of 1.0% steel fibers on mechanical properties of concrete gives larger values than the non-fibrous concrete by (27%, 33%, 32%, and 18% 8) The ultimate load of fibrous concrete beams is greater than beams without steel fiber by (33-100) % for shear behavior. 9) The ultimate load of fibrous concrete beams is greater than beams without steel fiber by (  33  -38  % ) for flexure behavior. 10) The deflection of NAC beams is smaller than RAC beams for the same parameters. 11) The deflection of beams with steel fiber is smaller than the control beams (NAC) and (RAC).

Conclusion
During the review of the results of this paper and the use of recycled aggregates produced from recycled concrete and that be replaced completely with natural aggregates in the concrete mixtures, several things can be concluded: 1. A decrease in resistance in general as to compressive strength , tensile strength and modulus of rupture addition to a decrease in the elastic modulus ,therefore .the Addition of different ratios of steel fiber can improve the magnitudes of this 2. Increment the vf of steel fibers due to the high tensile strength and competency of steel fibers to arrest micro-cracks and break the propagation of cracks until the composite ultimate stress of SFRC is extended . 3. The use of recycled concrete aggregate makes reduce in workability of concrete because the recycled aggregate consists of natural aggregate in addition to the old cement mortar so its effectiveness and its high ability to absorb mixture water. Therefore, the use of high water reduces materials would be useful in solving this problem . 4. During the flexural and shear test under the monotonic load, the shear failure during the review of the results of this paper and increment the vf of steel fibers due to the high tensile strength and competency of steel fibers to arrest micro-cracks and break the propagation of cracks until the composite ultimate stress of SFRC is extended . 5. The use of recycled concrete aggregate makes reduce in workability of concrete because the recycled aggregate consists of natural aggregate in addition to the old cement mortar, so its effectiveness and its occurs suddenly, while the flexural failure occurs gradually and the deflection continues for several readings after failure.