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Procedía Engineering 125 (2015) 825 - 831
Procedía Engineering
www.elsevier.com/locate/procedia
The 5th International Conference of Euro Asia Civil Engineering Forum (EACEF-5)
The effect of combination between crumb rubber and steel fiber on impact energy of concrete beams
Ahmed Tareq Noamana*, B.H. Abu Bakara, and Hazizan Md. Akilb
aSchool of Civil Engineering , Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia bSchool of Materials & Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, 14300, Penang, Malaysia
Abstract
The effect of combination between crumb rubber and steel fiber on low-velocity impact energy of concrete beams was determined in this study. Crumb rubber ranging in size from 1-2 mm was recycled from waste tires. This rubber was then incorporated into normal concrete (NC) and steel fiber concrete (SFC) mixes by partially replacing fine aggregate at two different ratios (17.5% and 20%) by volume. The beams examined in this study measured 500 mm x 100 mm x 100 mm. They were fabricated from NC and SFC with a volume fraction of 0.5% hooked-end steel fiber. A low-velocity drop hammer with a mass of 5.1 kg was dropped repeatedly from a height of 0.17 m until the initial crack was generated. The process continued until beam failure. Impact energy improved considerably at both initial crack and ultimate failure through the combination of steel fiber and crumb rubber. However, the partial replacement of fine aggregate by volume with crumb rubber reduced the compressive strengths of both NC and SFC mixes. Nonetheless, the synergy between crumb rubber and steel fiber is determined in this study for producing concrete with the desired properties, as well as to introduce an applicable solution for the problem of discarded tires.
© 2015 The Authors. Published by ElsevierLtd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).
Peer-reviewunder responsibility of organizing committee of The 5th International Conference of Euro Asia Civil Engineering Forum (EACEF-5)
Keywords: Rubberized concrete; hooked end steel fiber; impact energy; low velocity impact.
1. Introduction
With the rapid increase in the automobile population, the problem of waste tires is an important consideration for many countries. The damping of used tires on land causes many serious economic and environmental problems, as
* Corresponding author. Tel.: +60133199035; E-mail address: atn_en@yahoo.com
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of organizing committee of The 5th International Conference of Euro Asia Civil Engineering Forum (EACEF-5) doi:10.1016/j.proeng.2015.11.148
reported by previous studies [1,2]. Thus, rigorous legal actions have been implemented by some countries to prevent the establishment of tire landfills [1]. Extensive studies have also been conducted on the utilization of the crumb rubber derived from waste tires, as well as on the incorporation of this rubber into concrete mixes. For instance, Batayneh et al. [3] partially replaced a volume of fine aggregate with crumb rubber measuring (0.15-4.75 mm). Although the mechanical properties were diminished as a result, the strength of the crumb rubber concrete mixes was within the requirements of lightweight concrete. Furthermore, an applicable technique was developed in this work to address the problem of discarded tires, which is a serious threat to third-world countries.
Subsequently, rubberized concrete has been commonly used by many authors to improve the dynamic behavior of concrete [4-7]. Forces caused by vibrations such as impact or shock loading from moving vehicles can be observed through the lifespan of concrete structures [4]. The desired properties of rubberized concrete are related to dynamic behavior; thus, steel fiber and crumb rubber have been combined under high-strain impact loading [8]. The size of rubber particles and a maximum replacement ratio of 10% improved the dynamic increase factor. In addition, this combination significantly enhanced dynamic properties. Sukontasukkul et al. [9] investigated the behavior of concrete panels subjected to shooting with bullets. The concrete panels consisted of steel fiber, and a rubberized concrete layer replaced a steel fiber of specific thickness within the crumb rubber at different ratios (50%, 75%, and 100%) by volume. The obtained results showed that the double-layer panels performed better under impact and acted as a cushioning layer that reduced the amount of impact force that reached the layer of steel fiber concrete (SFC). Steel fiber and crumb rubber were also combined recently to study the mechanical properties and fracture toughness of recycled concrete aggregates with different ratios of crumb rubber [10,11]. The results obtained in these studies suggested the potential improvement of fracture toughness through the use of crumb rubber and steel fiber in such aggregates. Moreover, a positive synergy of different engineering properties can be observed by combining these two materials [12].
In the current study, impact resistances at initial crack and ultimate failure are introduced for rubberized mixes. Fine aggregates are partially replaced by crumb rubber at the replacement ratios (17.5% and 20%) by volume. The effect of combination between crumb rubber with hooked ended steel fiber with at the aforementioned replacement ratios on the impact energy of concrete beams is determined as well. The obtained results are compared with those derived given NC and SFC mixes.
2. Experimental Work
2.1. Materials and mixing
In this study, normal concrete mix is consisting of ordinary Portland cement (OPC) with specific gravity 3.15, coarse aggregate, and fine aggregate with specific gravities 2.65, 2.64, respectively. The maximum coarse aggregate size was 14 mm, natural sand used as fine aggregate. The crumb rubber is recycled from worn out tires and have size (1 - 2) mm (Fig. 1(a)), while specific gravity 0.73. Hooked end steel fiber (Fig. 1(b)) with aspect ratio 80 and diameter 0.75 mm was used for concrete mixes with steel fiber. Superplasticizer used to maintain the workability of concrete mix. The concrete specimens were prepared with 17.5% and 20% replacements ratios by volume of fine aggregate while the steel fiber ratio kept constant 0.5% as a volume fraction.
The total number of mixes was 6 mixes, ordinary, steel fiber, rubberized, and steel fiber rubberized concrete (Table 1). Cubes, 100 mm side were prepared for the compression test, while six beams for each mix, 500*100*100 mm, were casted to determine the impact energy. All samples were cured in water for 90 day until testing.
2.2. Testing and procedure
As continuity to the work conducted previously by Al - Tayeb et al. [6,13], the fabricated rig, Fig. 2, was used to conduct the low velocity impact test. This rig consisting of a hammer with weight of 5.1 kg and dropped from a height of 0.17 m which gives impact energy 8.5 J approximately. The impact energy where determined based on the number of drops that cause first crack and ultimate failure.
(a) (b)
Fig. 1. Images of the materials used (a) crumb rubber particles (1 - 2) mm; (b) hooked end steel fiber.
Table 1. Mix proportions considered in this study (kg/m3).
No Mix Cement Coarse aggregate Fine aggregate Steel fiber Crumb rubber Superplasticizer Water
1 NC 430 907 814 - - - 202
2 SFC 430 907 814 39 - 1.5 202
3 RC17.5 430 907 670 - 39.5 - 202
4 RC20 430 907 650 - 45.3 - 202
5 SRC17.5 430 907 670 39 39.5 1.5 202
6 SRC20 430 907 650 39 45.3 1.5 202
The impact energy IE can be determined at any number of blows (N) by using the following equation [14]:
IE = NMgH (1)
Where:
N = Number of blows until first crack or failure M= mass of the hammer = 5.1 kg H= height = 0.17 m
g= the gravitational acceleration = 9.81 m/sec2
The effect of friction between the falling hammer and the two guided rails will be taken equal to (0.9g) [6] .The energy equation is:
IE = NM (0.9g )H (2)
3. Results and discussion
3.1. Compressive strength
The results for compression strength at 90 days are shown in Fig. 3. Although the addition of steel fiber to concrete mixes causes improvement in this strength, crumb rubber reduced the compressive strengths of both NC and SFC mixes. A previous study reported that compressive strength was not enhanced significantly at 28 days given a 0.5% dosage of hooked-end steel fibers with an aspect ratio of 80 and a diameter of 0.75 mm [15]. By contrast, steel fibers positively affected compressive strength in the current study. Rubberized concrete RC17.5% and RC20% exhibited
results that were poorer than those of a normal concrete mix by 30% and 32%, respectively. Previous studies also indicated a reduced compressive strength of approximately 24% at 90 days when 1 mm of crumb rubber concrete replaced fine aggregate at a ratio of 20% by volume [13]. SRC17.5% and SRC20% mixes generated roughly 28% and 29% lower compressive strength, respectively, than the hooked-end SFC mix. In general, the rubberized steel fiber concrete mixes showed a higher compressive strength than NC and rubberized concrete mixes due to incorporation of hooked end steel fiber.
Fig. 2. Impact test rig with the specimen.
Fig. 3. Compressive strength results.
3.2. Impact energy (at first crack and ultimate failure)
The impact of concrete beams test results are presented in Table 2. The average number of blows for first crack and ultimate failure are listed in the same table. The impact resistance was found to increase for SFC by incorporation of hooked-end steel fiber. In addition, rubberized concrete mixes RC17.5 and RC20 showed higher results in
comparison with NC. By combination with steel fiber, the number of blows at first crack increased to 40 and 43 for SRC17.5 and SRC20 respectively. Same trend was noticed at ultimate failure when the number of blows increased to 68 and 72 for the above mentioned mixes, respectively.
Table 2. Impact test results.
First crack resistance (blows)
Ultimate failure resistance (blows)
Impact energy at first crack Impact energy at ultimate failure
(J) (J)
NC SFC RC17.5 RC20 SRC17.5 SRC20
14 40 43
10 45 19 21 68 72
42.5 156.2 98.9 108.2 307.6 330.0
347.8 145.3
163.9 527.2 558.9
As shown in Figs. 4 and 5, impact energy at both initial crack and ultimate failure improved when a specified volume of fine aggregate replaced by crumb rubber particles. Resistance at initial crack increased by 133% and 155% for RC17.5% and RC20%, respectively, whereas that for the steel fiber mix improved by 268%. The combination of crumb rubber particles with steel fiber displayed a different trend; impact energy at initial crack was 97% and 111% higher for SRC 17.5% and SRC20%, respectively, than for SFC.
The impact energy of the rubberized mixes at ultimate failure were 84% and 108% higher than that of the normal concrete mix. Impact energy at the ultimate or final crack was 52% and 61% higher for rubberized steel fiber concrete than for the steel fiber mix. Mixes with steel fiber generated favorable results due to the incorporation of hooked-end steel fibers into the concrete mix. The rubber particles increased ductility, whereas the addition of the steel fiber improved bonding under cracks. Further improvement in steel fiber concrete was achieved by crumb rubber. This led to a positive combination between rubber particles with industrial steel fibers.
Fig. 4. Impact energy at first crack.
Impact energy at initial crack was found to increase by 145% when 1 mm crumb rubber partially replaced fine aggregate by volume at a ratio of 20% in rubberized concrete [6]. Owing to rubber particles size, the crumb rubber with 1 mm showed further improvement in impact energy by 19% at first crack for this ratio in comparison with fine
crumb rubber (0.4 - 1) mm. Thus, encourages incorporating greater size as investigated in this study. Further investigations for higher replacement ratios could be also presented in the future.
Fig. 5. Impact energy at ultimate failure.
Moreover, the addition of steel fibers to concrete enhanced many of the properties of the latter, such as dynamic behavior [16] and tensile properties [17]. Combination with crumb rubber improves these properties further as mentioned earlier. The cumulative effect of steel fiber and crumb rubber under tensile loading has been reported previously [18]. The role of steel fiber is not only enhancement of the first crack resistance; an increase in the post crack resistance was achieved as seen in this work. While the crumb rubber particles considerably improve the ductility of normal concrete and this sustain further energy absorption [6]. The combined effect between them on the improvement of impact energy was attributed to the increase in the peak strain and the toughness (area under stress -strain diagram) that could result improvement in the impact resistance of concrete [8].
Thus, the synergy between SFC and crumb rubber particles can be considered in further investigations into the properties of concrete.
4. Conclusions
Fine aggregate was partially replaced with crumb rubber to determine the impact energy at the initial crack and ultimate failure of normal and steel fiber concrete beams. The weight selected for impact loading applied on concrete beams was 5.1 kg. The replacement ratios of crumb rubber were 17.5% and 20% by volume of fin aggregate. When crumb rubber was added to normal concrete, the impact resistance was enhanced by increase in the number of blows to cause first crack as well as the ultimate failure. When crumb rubber was incorporated into SFC, impact energy was higher than that of hooked-end SFC. In all cases, the impact energy of rubberized concrete mixes was superior to that of normal concrete. The increase in the rubber content affected the impact energy positively at first crack and ultimate failure for both NC and SFC. Thus, a cumulative effect was achieved by combination with hooked - end steel fiber.
Therefore, the results obtained in the current work can indicate how steel fiber and crumb rubber work together to improve the dynamic properties of concrete. Nonetheless, other properties, such as compressive strength, decline in the process. Hence, this research direction must be investigated further.
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