EFFECT OF RECYCLED MATERIALS AND HYBRID FIBERS ON THE PROPERTIES OF SELF-COMPACTING CONCRETE

Self-compacting concrete (SCC) has many properties comparing to conventional concrete and represents a good choice towards sustainability. The use of different recycled materials contributes to seize the negative impact of huge amount of waste on the ecosystem. In this study, locally available materials have been used as partially cement replacements. Such materials including ceramic waste powder (CWP) and glass powder (GP) in addition to fly ash with total cement replacement of 30%(12%CWP+8%GP+12%Fly ash) have been found to increase the compressive strength by about 7% compared to the control SCC. Normal aggregate was replaced by recycled aggregate with different recycled aggregate which are Recycled Concrete (RC), Crushed red brick (REB) and Crushed ceramic (CER.) The percentages of replacements are: 25%, 50%, 75% and 100%, for each type of aggregate. The results show that the increase of the amount of recycled aggregates decreases the strength properties of SSC and effect on workability of SSC also the result show a reduction in oven dry density. The combination of different type of recycled aggregate shows a reduction in SSC strength. The use of fibers shows better performance of SSC compared to combination aggregate mix without fiber but reduce the workability of SCC. However, the fiber content of 1.0% shows the best result of the mechanical properties, whereas, fiber content up to 1.5% affects negatively on concrete properties. The use of hybrid fiber also increases the strength properties of concrete.


INTRODUCTION
Conventional concrete technology requires mechanical vibration for placing concrete, which is time-and energy-consuming, noisy and often dangerous. In order to overcome these issues, self-compacting concrete (SCC) is developed, However, facing growing demands related with a sustainable development, technology of self-compacting concrete becoming questionable for the reason of its relatively high content of cement which can cause high heat of hydration danger of quick setting, also that cause an increased value of carbon footprint also as we mention before there is huge quantities of construction and demolition waste which represent a real challenge to environmentalist so recycling this waste can effectively contribute to manage these waste Also there another problem related to the concrete which is brittleness nature of concrete the using of the fiber will help to overcome this problem because of the Abundance of raw materials the using of conventional building materials is more traditional so hope this research carried out and the using of recycled material become more acceptance. [1][2][3][4][5][6] This study aimed to design self-compacting concrete reinforced with hybrid fiber (recycled plastic and sisal fiber) and study the effect of using different recycled material as partial replacement of cement and to investigate the effect of using different recycled aggregate on the behavior of concrete of both fresh and hardened properties.

EXPERIMENTAL PROGRAM
This section covers the materials used and the tests done. *eethardawood@ntu.edu.iq

Materials used
Cement: Ordinary Portland cement (OPC) Type I used in this study has been manufactured from Badoosh factory. Its physical characteristics and chemical compositions are illustrated in Tables 1 and 2, respectively.

Fine aggregate:
The sand used in this study was the natural river sand from Kanhash region in Mosul city with specific gravity of 2.63.

Test
Produced cement ASTM C150 [7] Initial       Table 3 to show the characteristics of it.

R1
Reference mix with 30% cementitious materials The percentages of each of fly ash, glass powder and ceramic powder are determined depending on mortar trial mixes to get the optimum percentages of combination

Fiber
Sisal fiber: Natural sisal fiber was used with length of 20 mm and aspect ratio of 40. Recycled plastic fiber: Recycled plastic from PVC factory where chopped into length of 20 mm and diameter of 2mm and aspect ratio of 10.

Mix proportion
The proper ties of SCC are affected by the material properties; the mix proportion was 1:1.60:1.40. The water to binder is 0.38 with total cementitious materials of 528kg/m 3 . The cement content is 368 kg, fly ash is 52.8, ceramic waste powder (CWP) is 63.6 kg, and glass powder (GP) is 42.2 kg. The designation of the mixes and mix proportions are depicted in Tables 4 & 5. The SCC mixes reinforced with fibers are listed in Table 6.
Mixing procedure: mixing procedure for SCC is more sensitive to the time comparing to the conventional concrete, the following procedure where performed to obtain a SSC: 1. Fine and coarse aggregates are loading and mixing at the beginning for 1 minute 2. Cement and filler are added and mixed for 1 minute. 3. A half of mixing water in addition to Sika visco-crete 5930 have been added and mixed for 2 minutes 4. The residual water and fibers are carefully added (to avoid balling) an mixed with 3 minutes. Casting and curing: After finishing the mix procedure the test of fresh concrete were done to conduct Slump and flow time v-funnel L-box tests.   The molds were used steel and plastic mold were lubricated and the specimens were cast only in one layer without any compaction. All specimens were kept in laboratory for (24±2) hours then demolded and immersed in water until the specific testing time.

MIXES
Test procedure: The tested fresh properties of SSC includes methods used for Filling ability, Passing ability and Segregation resistance (slump flow, L-box and V -funnel tests), respectively. Whereas, the hardened SCC tests includes compressive strength test which was carried out on 100x100x100 mm cube specimens based on BS 1881: part 5 [9]. The average of three specimens was recorded and considered for each age test (7, 28 and 90 days). The splitting tensile strength was performed in accordance with ASTM C496 [10] and conducted on cylinders of 100 * 200 mm. The average of three test specimens has been taken at 7, 28 and 90 days. Also, the flexural strength test was done according to ASTM C78 [11]. The flexural strength was carried on 100*100*400 mm prisms. The flexural value was taken as the average value of three specimens at 7, 28 and 90 days. The dry density concrete for SCC in a hardened state at age 28 days was carried out in accordance with ASTM C 642 [12]. Lastly, the Ultrasonic Pulse Velocity (UPV) Test was performed on specimens at age of 28 day. The test was carried out in accordance with ASTM C597 [13].

RESULTS AND DISCUSSIONS
This section deals with the analysis of the results which were obtained after testing all the specimens and their dis-     Table 7 shows the results of different SCC mixes prepared by various recycled aggregates. From this Table, it can be noticed that the slump value ranges from 630 mm to 733mm. While the T500 ranges from 2.57 to 4.0 sec, the v -funnel ranging from 7.5 sec to 11 sec and L-box varies from 0.72 to 0.9. From the results, it can be observed that amount of recycled aggregate would reduce the workability. This may return to the shape of this aggregate and the reduction of free water in SSC which is the main dominant of the recycled aggregate. The lowest value of flow has been obtained when the normal aggregate was completely replaced by crushed ceramic. Whereas, the crushed clay bricks aggregate show the best value among the recycled aggregate. Adding CWP, GP, Fly ash show a slight decrease in flow diameter and this may be related to the SSC become more viscous. The Table 8 shows the test results of workability for the fiber mixes of sisal fiber, plastic fiber and hybrid fiber. It can be seen that the increase in Vf of fiber reduces the slump value from 681mm to 640mm for the mixes SF1 and SF2, while the v-funnel result ranges from 11 to 13 sec and the L-box ranging from 0.77 to 0.

Hardened properties
Compressive strength Table 9 shows the compressive strength of mixes of recycled concrete aggregate in addition to the reference value. From such Table, it can be observed that the use of RC reduces the compressive strength of SCC and this may be due to the low property of RC aggregate compared with normal aggregate. Also, it can be noticed that the increase of the crushed clay brick amount, reduces the compressive strength at all age of concrete. This reduction is related to the reduction in adhesive strength between surface of particle of crushed clay brick and cement paste also may related to the difference of shape and size between natural aggregate also the reduction may also related to low strength properties of clay brick [14]. The incorporating of ceramic aggregate causes a reduction in compressive strength and this reduction may attributed to the weak bond between CER aggregate and cement paste and the shape of CER aggregate make a continues path of porosity which led to un dense concrete the reduction was at all age of concrete [15].

Density and ultra pulse velocity (UPV)
From Table 15, it can be found that the UPV values depend on the density. Hence, the increase in UPV values was comparable with the increase in density values for SCC prepared from recycled aggregate with or without fibers.

CONCLUSIONS
Some conclusions are revealed for this study which deals with the production of Self Compacting Concrete (SCC) as follows: 1. There is ability to replace normal aggregate with recycled aggregate (recycled concrete aggregate, crushed ceramic, crushed clay brick) up to 25% without significant influence of concrete properties. 2. The crushed ceramic aggregate gives the lowest strength values compared with other types of aggregate. 3. The increase in recycled aggregate reduces the workability, oven dry density and strength. 4. Sisal fiber can be used to improve splitting and flexural strength. However, the plastic fiber can be used up to 1% to give best result and the hybrization of two type fiber improves strength properties.