Eco-friendly concrete produced with recycled materials

Using recycling materials to produce concrete become a major subject for research in the last decades. The work aims to examine the effects of the partial replacement of fine aggregate by recycled rubber. In addition to studying the influence of two different fiber types on mechanical properties of concrete with rubber replacement. Three types of rubbers that differ in particle size are used to find the effect of rubber particle size on compressive strength, splitting tensile strength, and flexure strength of the concrete mix. Two waste fiber types are used which are Rope Waste Fiber (RWF) and Steel Waste Fiber (SWF). The findings showed that minimizing the rubber particle size improved the mechanical properties. Also, using two types of waste fiber (rope and steel) together led to improve compressive strength.


Introduction
A huge number of waste tires were buried or thrown away in the world yearly, which causes crucial threats to the environment.The disposal of these tires (waste) has converted into a serious environmental issue.For discarded waste tiers there are several ways: landfilling, burning, or using in sports grounds as a mulch and asphalt modifier.Many problems are associated with stockpiled tires like pollution of water, air, and soil in addition to economic, health, and environment.One of the most important directions of research recently is utilizing waste ties in the mortar and concrete production.Concrete consumes a high amount of natural sources for saving so it should go ahead toward sustainability by using alternatives (waste materials) [1,2].The reasonable solution is to use the disposed of tire (waste rubbers) as an aggregate replacement for concrete production for an environment-friendly program.The green concrete (concrete with recycled materials) can be used in many construction projects like structural building, paving of roads and other projects [3,4].
Eshmaiel Ganjian et al. 2009 [4] presented the ability to use 5%, 7.5%, and 10% of waste tire rubber in concrete as cement and aggregate replacement.The findings explain that compressive strength illustrated a decoration with increased wasted rubber content.The tensile strength for a mixture that had aggregates replacing was lower than a mixture that had a powder rubber as cement replacement.Issa, & Salem 2013 [5] investigated the concrete mechanical properties having tire rubber (recycled) as fine aggregate ranging between 0 to 100%.The experimental result presented that 25% of recycled rubber replaced with natural aggregate gives fine compressive strength.While concrete density showed a reduction with increasing rubber content.Faraz et al. 2015 [6] investigated the influence of crumb rubber as 5% and 10% of coarse aggregate replacement on concrete.The find out of this work was that concrete workability showed increasing with utilizing waste rubber.The concrete unit weight presented a clear reduction while the compressive strength illustrated increasing at earlier ages and reduction at later.Aiello et al. 2009 [7] reported there is slight improvement compressive strength when utilize waste steel fiber in concrete at different percentage and that agree with Yazici et al. [8].Malagavelli, and Rao, 2010 [9] studied the effect of utilizing waste plastic fiber on the concrete mechanical properties.Compressive strength presented an increase of 5% when fiber content 1%.Flexural strength exhibit a satisfy results as compared with the reference mix.Nibudey et al, 2013 [10] investigated the influence of waste plastic fibers on concrete at a different dosages ranging from 0 % to 3 % with aspect ratio 35 and 50.The results presented that the workability showed a reduction with increasing plastic fiber content in addition to the density presented the same behavior of workability.Compressive, flexural, and split tensile strength with 1% of waste plastic fiber was increased by 5.26 %, 17.32%, and 15.47% respectively with 35 aspect ratio.And 7.35%, 24.10%, and 24.91 increase for compressive, flexural, and split tensile strength with 1% of waste plastic fiber at 50 aspect ratio respectively.
This work focuses on utilizing different waste materials (waste tire rubber as partial sand, steel fiber from waste tires, and waste plastic fiber) for the production of eco-friendly concrete.The slump test and mechanical properties (compressive, split, and flexural strength), in addition to concrete density are conducted.

Research Significance
Huge amount of waste tire damping in Iraq, and that amount increased yearly with increasing population.These waste tires cause serious environmental problems in case not managed correctly.On the other hand, a massive quantity of virgin materials consuming for concrete production.For that one of the brilliant solutions utilize waste tire for sand saving as well as the steel fiber from waste tire used for improving concrete characteristic.Also, waste Rope is used as waste fibers in concrete.

Material Properties
For production the concrete mixes in this work, many materials were used as mentioned below: Portland cement (Ordinary Type II), known commercially by KARASTA which is conforming to Iraqi specification No. 5 [11].The chemical, physical and mechanical characteristics of cement are tabalated ted in table 1. Natural sand (fine aggregate) provides from local quarries.The sand with grain zone 3 in SSD condition.The sieve analysis of sand can show in table 2. Crushed gravel from Al-Nabaei region with a maximum size of 20mm was utilized (gravel and sand conformed to Iraqi specification No. 45 [12]).The gravel serving is illustrated in table 3. Local tap water is used for specimens mixing and curing (clear water).Rubber from waste tires, where used as a natural fine aggregate partially replacement.Waste rubber with three sizes (0-1mm), (1-3mm) and (3-5mm) which are shown in figure 1. Steel Waste Fibers (SWF) were obtained by cutting steel fibers extracted from damaged tires into small pieces (20-30 mm in length) as presented in figure 2. Rope Wste Fibers (RWF) were obtained by cutting polymeric rope fibers (0.34 mm in diameter) into small pieces (20-30 mm in length) as illustrated in figure 3.

Experimental Methodology
Different concrete mixtures were conducted under laboratory conditions for determining fresh characteristics and the properties of the mechanical hardened concrete.The water/cement was 0.5.The reference mixture consisted with 100% of natural sand, and the other mixes involved replacing sand with waste tier rubber, by 4%, with different ranging of partical size [size(0-1)mm, size (1-3)mm and size(3-5)mm] respectively.Table 4 illustrated the proportions mixture details for concrete in this work.Steel fiber from waste tire and plastic fiber from waste rope were used by 1% separately in each mix (mixture C and D) and together by 1% at mixture E for improving concrete properties.
The mixing procedure for concrete was including dry mix for fine and coarse aggregate together then adding Portland cement and continuing the mixing then after adding the water and mixing for 3 minutes.For mixtures that have fiber the mixing continued till the mixture be homogeneous.Directly after mixing, the slump value was investigated for fresh concrete according to ASTM C143 [13].Then after, fresh mixes were cast in the molds and vibrated very well.When 24 hours were elapsed the molds were removed and stored the specimens in a water tank for curing till the test time.Compressive strength was tested at 7 and 28 days.Also, splitting tensile, flexural strength and bulk density were conducted at 28 days.The experimental tests consist of the following specimens: • 42 cubes (six for each mix) to get the compressive strength at ages 7 and 28 days ; • 21 cylinders (three for each mix) for getting the splitting tensile strength; • 21 prisms (three for each mix) to get the modulus of rupture.

Slump test for tested mixes
The slump was tested for all fresh mixes.Figure 4 and table 5 presented the concrete flowability with the replacement of the rubber as aggregate to produce concrete.The slump was decreased when rubber was used by about 10%,20%, and 16% for B1, B3, and B5 mixes respectively compared with the reference concrete mix.The decrease in slump value for mixes with the bigger size of rubber particles (B2 and B3) was more than B1.Because of the irregular forms and sharp edges of rubber particles, the slump values are reduced when rubber aggregate is used.These sharp edges are less for rubber with smaller sizes.On the other hand, adding steel fiber or plastic fiber led to increase the concrete slump by 11% as comparing with mixture B1.The mixture that has a combination of two types of fiber presented an improving in slump by 48% as regarding the same mixture without fiber.
Table 5. Slump values for all tested mixed.

Compressive strength for tested mixes
The compressive strength was measured on 42 cubes of size (100*100mm).Where: • 21 cubes (3 for each concrete mix) are examined for getting the value of compressive strength value at age of 7 days; • 21 cubes (3 for each concrete mix) are tested for getting the compressive strength value at age of 28 days; The findings for all mixes can be noticed in table 6.The compressive strength results for the tested mixes are tableted in figure 5.The 7 days compressive strength decreased when fine aggregate was replaced with rubber according to the reference concrete mix; the decrease in the compressive strength is 25.6%, 41%, and 50% for B1, B3, and B5 respectively.At 28 days, the compressive strength illustrated 23.3%, 26.1%, and 42.6% for B1, B3, and B5 respectively as regards to control mixture A. This attribute may be due to the modulus of elasticity of rubber which is lower than the natural sand in addition to poor bonding and adhesive between rubber particles and cement matrix [14].As presented in figure 5 the compressive strength showed a reduction with increasing the size of rubber aggregate from (0-1 to 3-5) mm.
The presence of fiber led to reducing compressive strength by 20.8% and 7.14% for concrete mix with RWF and SWF respectively compared to the fiber-free mixture B1.While there is an enhancement in compressive strength by 2.5% when the mix of RWF and SWF was used compared with B1 mix at 7 days.And at 28 days the compressive strength exhibits a reduction by 22.7% and 3.6% for mixture C and D respectively as compared with B1.Otherwise, the increasing in compressive strength was 4.8% for the mixture having two types of waste fiber as compared with the same mixture without fiber (B1).

Splitting Tensile Strength
Splitting tensile strength property is measured as the requirements of ASTM C 496/C [15] with a cylinder diameter of 100 mm and 200 mm for height.Splitting strength test is measured by equation ( 1): Where : ft: is the splitting tensile strength in (MPa), P: the maximum load that applied (N), d: cylinder diameter in mm, l: length of the cylinder in mm.
The results of splitting at 28 days showed table 7 and figure 6.The splitting tensile strength showed a reduction with utilizing rubber as 4% of natural sand replacement.The reduction was 25.4%, 12.7%, and 11.1% for mixtures B1, B3, and B5 as compared with reference mixture A. The interlock between the rubber aggregate and cement matrix is poor and micro cracks are generated fastly due to the weakening of the interfacial transition zone (ITZ), for that the concrete failure under tension happened clearly as compared with the control mixture [16].
Fiber adding with 1% led to improve splitting tensile strength by 40.6%, 49.1%, and 32.6% for waste plastic fiber, waste steel fiber, and the waste plastic and steel fiber together respectively.These results may be due to the high tensile strength of waste steel fiber compared with waste plastic fiber, so the concrete with steel fiber presented higher tensile strength [17].
(2) Where: fr: is flexural strength (MPa), P: ultimate load that applied (N), l: span length in mm, b: prisms width in mm, d: prism depth in mm.
The experimental results showed an improvement in the modulus of rupture for concrete containing 4% waste tire rubber as fine aggregate.The increase was 44.3%, 34.5%, and 29.6% for mixture with rubber size (0-1)mm, (1-3)mm, and (3-5)mm respectively as compared with control mixture A (with zero rubber aggregate).
Table 8 and figure 7 presented the modulus rupture results at 28 days.When waste fiber was utilized by 1%, the concrete flexural strength showed a reduction of 6.7%, and 8.26% for WSF and WRF respectively, while there is an increase of about 2.16% for the mixture with 1% of waste steel and plastic fiber comparing with the same mix but without fiber.

Dry Density
The density of concrete was conducted with cubes with 100mm according to ASTM C 642 [19].The findings of the previous studies indicated that utilizing waste tire rubber led to reduce the concrete density.The naturally of rubber has low specific gravity as regarding with natural sand [20].In present work, the results showed that the size of waste tire rubber as a fine aggregate showed the lowering of concrete density with increasing the size of rubber.The reduction in density was 4.3% and 5.6% for rubber size (1-3)mm and (3-5)mm as compared with rubber aggregate size (0-1)mm at 4% content.When fiber is added by 1% the concrete density is not clearly affected specially with waste plastic fiber.

CONCLUSION
The present work is aimed to utilize three types of waste (waste tire rubber as sand, waste steel and waste plastic as fiber) for concrete production.The major conclusions depending on the experimental results are as follows.
1-Concrete slump showed a reduction with using waste tire rubber as fine aggregate while by increasing the rubber size the slump was reduced.Adding 1% fiber (steel or plastic) have no adverse effect on the slump of concrete.
2-The concrete compressive strength was lowered by utilizing waste tire rubber at 4% as a fine aggregate.The strength reduction increase with increasing size of rubber.Adding fiber 1% led to reduce the compressive strength for steel or plastic fiber separately while when using the steel and plastic fiber together led to improve compressive strength.
3-The splitting tensile strength presented a a 4-with replacing 4% of natural sand by waste tire rubber as well as, the splitting tensile strength increased with increasing the size of rubber particles.
5-Modulus rupture exhibited an increase with 1% of fiber especially waste steel fiber more than waste plastic fiber at the same content as compared to the control mixture

Table 3 .
Sieving analysis of coarse aggregate.