Lightweight concrete application in construction field is growing rapidly in these recent years due to its advantages over ordinary concrete. In this paper, pumice breccia which can be found abundantly in Indonesia is proposed to be utilized as the coarse aggregate. In spite of its benefits, lightweight concrete exhibits more brittle characteristics and lower tensile strength compared with normal concrete. On the other hand, fiber addition into concrete has become widely used to improve its tensile properties. Furthermore, the utilization of hybrid fiber in a suitable combination may potentially improve the mechanical properties of concrete. This paper experimentally examines the effects of hybrid polypropylene-steel fiber addition on some hardened properties of pumice breccia aggregate lightweight concrete. Five groups of test specimens with fixed volume fraction of polypropylene fiber combined with different amounts of steel fiber were added in concrete to investigate the density, compressive strength, modulus of elasticity, splitting tensile strength, and the modulus of rupture of the concrete mixtures. Test results indicate that hybrid fiber addition leads to significant improvement to the compressive strength, modulus of elasticity, splitting tensile strength, and the modulus of rupture of the pumice breccia lightweight aggregate concrete and meet the specification for structural purposes.
Lightweight concrete (LWC) application in construction field is growing rapidly in these recent years both for structural and nonstructural purposes due to its advantages over ordinary concrete. The demand for lightweight concrete in many applications of modern construction is increasing, owing to the advantage that lower density results in a significant benefit in terms of load bearing elements of smaller cross sections and a corresponding reduction in the size of the foundation. The maximum density of concrete which can be classified as lightweight concrete in some European construction codes is limited to 2000 kg/m3 [
In spite of its benefits, lightweight concrete exhibits its brittle characteristics and lower tensile strength compared with normal concrete. On the other hand, fiber addition into concrete mixes becomes more widely used to improve concrete tensile behavior. The geometrical size and modulus of elasticity of fibers are the main factors which will affect the performances of fiber reinforced concrete. In order to optimize the benefits of fiber addition in concrete construction, the application of different fiber types into fresh concrete mixtures was introduced and commonly known as hybrid fiber reinforced concrete (HyFRC). It becomes more popular in these recent years and expected to provide better physical and mechanical properties in concrete for structural purposes. The use of different types of fiber in a suitable combination may potentially improve the mechanical properties of concrete and result in synergic performance [
The main objectives of this research include (1) developing hybrid fiber reinforced lightweight concrete mixtures which should be suitable for structural applications using locally available materials, (2) examining the properties of the developed fiber reinforced lightweight concrete mixes, including demoulded density, compressive strength, modulus of elasticity, splitting tensile strength, and the modulus of rupture, and (3) studying the flexural load-displacement behavior of the lightweight concrete with hybrid fiber addition.
In this research, polypropylene fiber (PPF) and steel fiber (SF) were chosen to be utilized as hybrid fiber. Polypropylene was used due to being inexpensive, inert in high pH cementitious environment, and easy to disperse. In this research, monofilament polypropylene with 18
The mixtures were prepared with blended cement containing 23.13% of SiO2, 8.76% of Al2O3, 4.62% of Fe2O3, 58.66% of CaO, 0.90% of MgO, 2.18% of SO3, and 1.69% of loss on ignition which satisfies the requirements in the Indonesian Standards for Pozzolan Portland Cement [
Mixture proportion.
Material | Mix type | ||||
---|---|---|---|---|---|
A | B | C | D | E | |
Water (lt/m3) | 225.00 | 225.00 | 225.00 | 225.00 | 225.00 |
Portland cement (kg/m3) | 455.00 | 455.00 | 455.00 | 455.00 | 455.00 |
Silica fume (kg/m3) | 45.00 | 45.00 | 45.00 | 45.00 | 45.00 |
Coarse aggregate (kg/m3) | 606.81 | 606.81 | 606.81 | 606.81 | 606.81 |
Sand (kg/m3) | 538.52 | 538.52 | 538.52 | 538.52 | 538.52 |
Superplasticizer (lt/m3) | 4.70 | 4.70 | 4.70 | 4.70 | 4.70 |
Set retarder (lt/m3) | 0.70 | 0.70 | 0.70 | 0.70 | 0.70 |
Polypropylene (kg/m3) | 0.90 | 0.90 | 0.90 | 0.90 | 0.90 |
Steel fiber (kg/m3) | 0.00 | 33.50 | 67.00 | 100.50 | 134.00 |
All those concrete variants will be evaluated and analyzed further, based on the reference LWC mixture which was added with 0.10% PPF and 0.0% SF. This reference mixture was chosen due to the fact that extensive use has been made in the construction industry for the application of short (<25 mm long) fibrillated or monofilament PPF to alter the properties of the fresh concrete, notably to reduce the extent of plastic shrinkage cracking should it occur. These fibers are typically 12 mm long by 18
In accordance with the above-mentioned theoretical prediction, the effect of PPF has been researched in respect of the properties of LWAC. In most cases, it was reported that PPF has no effect on the compressive strength of LWAC. The addition of PP fibers in volume fractions lower than 1% does not significantly increase the splitting tensile strength of sanded LWAC and does not significantly affect the flexural strength and toughness. They demonstrated that this might be due to the lower tensile strength of PP fiber and also the weaker bond between PP fibers and the cement matrix [
Fresh characteristics of concrete mixes were evaluated using slump test method based on ASTM C-143 [
In this research, the effect of steel fiber addition on the workability of polypropylene fiber-reinforced lightweight concrete was evaluated using slump-test method based on ASTM C-143 [
Effect of steel fiber addition on the workability of HyFRLWC with pumice breccia aggregate added with 0.1% PPF and various volume fractions of SF.
In order to evaluate the effects of hybrid polypropylene and steel fiber addition on hardened properties of LWC with pumice breccia aggregate, the compressive strength, modulus of elasticity, splitting tensile strength, and the modulus of rupture of the concrete specimens were tested after 56 days of water immersion to achieve more representative results of concrete strength since all the mixtures were added with silica fume. Table
Effects of hybrid polypropylene-steel fiber addition on hardened properties of LWC with pumice breccia aggregate (mean ± standard deviation).
Volume fraction of steel fiber |
Demoulded density |
Compressive strength |
Modulus of elasticity |
Splitting tensile strength |
Modulus of rupture |
---|---|---|---|---|---|
0.0 | 1764.78 ± 5.92 | 16.45 ± 0.35 | 7317.49 ± 396.18 | 1.24 ± 0.07 | 2.78 ± 0.16 |
0.5 | 1857.33 ± 16.18 | 19.15 ± 0.43 | 9125.91 ± 353.25 | 2.56 ± 0.12 | 4.45 ± 0.22 |
1.0 | 1874.06 ± 10.45 | 20.14 ± 0.54 | 8191.96 ± 409.67 | 3.06 ± 0.03 | 7.16 ± 0.36 |
1.5 | 1902.09 ± 17.53 | 19.71 ± 0.64 | 7492.72 ± 657.91 | 3.99 ± 0.23 | 8.00 ± 0.73 |
2.0 | 1932.86 ± 3.74 | 18.56 ± 0.41 | 6836.53 ± 872.73 | 3.76 ± 0.18 | 7.98 ± 0.72 |
Effects of fiber content on demoulded density of hardened lightweight pumice breccia aggregate concrete can be observed in Figure
Effect of steel fiber addition on the demoulded density of HyFRLWC with 0.1% PPF and various volume fractions of SF.
Even though the demoulded density of HyFRLWC with pumice breccia aggregate increases due to the presence of steel fiber, it can be observed that the density of the lightweight concretes with hybrid polypropylene and steel fiber addition up to the combination of 0.1% PPF and 1.5% SF is still acceptable to be classified as lightweight concrete based on the maximum limit of lightweight concrete density which is required in the Indonesian national standard and most of the international standards.
Compressive strength evaluation of hardened HyFRLWC with pumice breccia aggregate can be found in Figure
Effect of steel fiber addition on the compressive strength of HyFRLWC with 0.1% PPF and various volume fractions of SF.
Modulus of elasticity of the hardened HyFRLWC with pumice breccia aggregate was also investigated at the same time with compression test as shown in Figure
Compressive strength and modulus of elasticity test setup.
Effect of steel fiber addition on the modulus of elasticity of HyFRLWC with 0.1% PPF and various volume fractions of SF.
In order to get more comprehensive results, the curves that show stress-strain relationship in concrete compression tests are also shown in Figure
Stress-strain behavior in compression tests of HyFRLWC with pumice breccia aggregate added with 0.1% PPF and (a) 0.0% SF, (b) 0.5% SF, (c) 1.0% SF, (d) 1.5% SF, and (e) 2.0% SF.
Test results which are related to the effects of hybrid fiber addition on the splitting tensile strength of hardened lightweight pumice breccia aggregate concrete can be observed in Figure
Effect of steel fiber addition on the splitting tensile strength of HyFRLWC with 0.1% PPF and various volume fractions of SF.
Experimental results which evaluated the effects of hybrid fiber addition on the flexural strength of hardened lightweight pumice breccia aggregate concrete can be observed in Figure
Effect of steel fiber addition on the modulus of rupture of HyFRLWC with 0.1% PPF and various volume fractions of SF.
Figure
Load-Deflection Behavior of Center-Point Loaded Simply Supported Beams of HyFRLWC with Pumice Breccia Aggregate Added with 0.1% PPF and (a) 0.0% SF, (b) 0.5% SF, (c) 1.0% SF, (d) 1.5% SF and (e) 2.0% SF.
Based on the tests results of the fresh and hardened properties of fiber reinforced lightweight pumice breccia aggregate concrete, the following conclusions can be drawn. In the fresh state of lightweight pumice breccia aggregate concrete, the addition of steel fibers consequently causes lower workability. The demoulded density of fiber-reinforced lightweight concrete tends to increase in accordance with the amount of steel fiber addition but generally can be classified as lightweight concrete based on most international standards of concrete structures. The compressive strength of lightweight concrete can be improved proportionally up to 22.44% when the hybrid polypropylene-steel fiber is added with the combination of 0.1% PPF and 1.0% SF then tends to decrease but still shows better performance compared to the reference concrete mixture. The modulus of elasticity also improved in accordance with the addition of hybrid fiber up to 24.71% when the concrete is added with the combination of 0.1% PPF and 0.5% SF then tends to decrease but is generally higher than the reference mixture. Higher splitting tensile strength of hardened fiber-reinforced lightweight concrete specimens can be obtained up to 222.28% when the hybrid fiber is added with a combination of 0.1% PPF and 1.5% SF then decreases after the optimum value but still achieves much higher strength compared to the reference concrete mixture. The modulus of rupture of fiber-reinforced lightweight concrete specimens can be improved proportionally up to 187.46% when the hybrid polypropylene-steel fiber is added with the combination of 0.1% PPF and 1.5% SF then decreases but still exhibits much better flexural performance compared to the reference concrete mixture.
The paper has not been previously published, is not currently submitted for review to any other journal, and will not be submitted elsewhere before a decision is made by this journal.
The authors highly appreciate the financial support from Universitas Negeri Yogyakarta (Yogyakarta State University) and partial material support which is provided by PT Bekaert Indonesia. The support of the Building Material Laboratory staff at the Faculty of Engineering, Universitas Negeri Yogyakarta, and their assistance in conducting the experimental works are also gratefully acknowledged.