Physico-mechanical and thermal performances of newly developed rubber-added bricks
Introduction
The building construction market is one of the most important and highly competitive markets in Europe. The new European energy regulation now considers a high standard of thermal protection in buildings with reasonable energy consumption, satisfactory thermal comfort conditions and low operational costs [1]. The typical U-values required by the national regulations in most European countries have been sharply dropped in the last two decades. This has caused increasing thermal insulation thicknesses in conventional building shells. Consequently, substantial percentage increase in structural cost and reduction in effective living space have been faced. The requirements have increased not only in terms of thermal properties, but also with respect to the environmental impact [2]. An issue that arises out of this activity a search for innovative, environmentally friendly and ready-to-use building composites that combine higher efficiency and quality in the building process with improved thermal resistance. This has set increased demands on the both thermal and mechanical (thermo-mechanical) performances of new building products integrated with various plasters, foils, particles and rubbers [3].
The large demand on building material industry has resulted from the increasing population, leading to a chronic shortage of building materials. The engineers have then been challenged to convert the industrial wastes to useful building and construction materials. Accumulation of unmanaged wastes is today's one of significant environmental concerns, especially in developing countries. Recycling of such wastes as building materials appears to be viable solution not only to such pollution problem but also to the problem of economical design of buildings. The increase in the popularity of using environmentally friendly, low cost and lightweight construction materials in building industry brings the need for searching more innovative, flexible and versatile composites. The most important aspects of innovation might be in the development of integrated insulation products [2], such as the insulated, reinforced concretes [4], two or three-wythe precast sandwich wall panels [5], and rubberized concretes [6]. Part of this interest is to establish the thermal performance of the alternative systems and products. Accurate thermal characteristics are required to guide product development and manufacturing. Methods and data exist for dealing with the common building walls and insulations, but new systems and products are generally lacking such data [2], [3], [4], [5].
One of the new and popular products in this sense is modified cementitious composites with scrap tire rubber [7]. Use of rubber from scrap tires in Portland cement concrete (PCC) mixtures can result in large benefits, like lower density, increased toughness and ductility, higher impact resistance, and more efficient heat and sound insulation. The use of recycled tire rubber in PCC also helps alleviate disposal problems and address the growing public concern about the need to preserve natural sand and aggregates [6], [7]. The recent introduction of European Union directives are in favor of this and include significant restrictions on the disposal of used tires in landfills, stockpiles, or illegal dumping grounds [8]. Accumulations of discarded waste tires have been a major concern because of waste rubber is not easily biodegradable even after a long-period landfill treatment and unmanaged waste tires represent an environmental and health risk through fire hazard and as a breeding ground for disease-carrying mosquitoes. The alternatives are thus oriented toward materials and energy recovery [7].
The literature about the use of tire rubber particles in cement-based materials focuses on the use of tire rubber as an aggregate in concrete and evaluates only the physico-mechanical properties [9]. Thermal behaviour of such products has not been examined in detail [3]. Mechanical test results have consistently indicated that despite its some beneficial features mentioned above, rubberized concrete mixtures posses lower compressive and splitting tensile strengths. The degree of reduction in strengths has been found to depend on the size, proportions and surface texture of rubber particles [7], [10], [11]. Eldin and Senouci [12] reported approximately 85% reduction in compressive strength and 50% reduction in splitting tensile strength when coarse aggregate was fully replaced by coarse crumb rubber chips. On the other hand, a reduction of approximately 65% in compressive strength and 50% in splitting tensile strength was observed when fine aggregate was entirely replaced by fine crumb rubber. These mixtures had the ability to absorb a large amount of energy under compressive and tensile loads. These trends of findings were independently confirmed by Topcu [13] in a later study. Topcu and Avcular [14], [15] reported that the impact resistance of concrete increased when rubber aggregates were incorporated into the concrete mixtures. Guneyisi et al. [16] showed the addition of the silica fume into the matrix improved the mechanical properties of the rubberized concretes and diminished the rate of strength loss. Their results also revealed a rubber content of as high as 25% by total aggregate volume might be practically used to produce rubberized concretes with compressive strength of 16–32 MPa.
The work presented herein focuses on the feasibility of using crumb rubber of scrap tires as aggregates in cementitious composites to develop ready-to-use brick with improved thermal insulation performance. A brick is the most basic building material for construction of low cost houses and multi-storeyed apartments. Conventional type of brick is made from burnt clay and a significant quantity of fuel is consumed during its production [17]. Rubber-added brick presented here eliminates this drawback since no fuel is necessary for its production. The recent estimates reveal that roughly 9,000,000 tires are discarded each year in Turkey, and less than 10% of these tires are currently recovered, leaving the rest to the environment [18], [19], [20]. Reusing these tires in brick sector of the country seems highly promising because nearly 57% of the building walls are constructed from bricks and similar type of light rectangular blocks [21]. This would contribute solving energy and environment concerns simultaneously since proper addition of waste rubber particles into brick results in better thermal insulation performance, as illustrated below.
Despite its potential advantage, not much attention has been given in investigating structural performance of rubber-added bricks. There is indeed limited number of researches on ready-to-use rubberized cementitious products in the construction applications: as concrete car barriers by Topcu [22] and as concrete pedestrian blocks by Sukontasukkul and Chaikaew [23]. The manufacturing processes for these applications were found to be economical, due to the simplicity in the production equipments. The literature is also remarkably scarce about quantifying thermal performance of any rubberized cementitious products although some degree of improvement in thermal insulation performance is clearly expected. The thermo-mechanical performances of ready-to-use rubber-added bricks examined here are intended to fulfil some of these gaps up to some extent.
Section snippets
Test samples
Crumb rubber used in this research is generated from waste tire section without steel fibre by using cracker mill process. It consists of particles ranging in size from 4.75 mm (No. 4 Sieve) to 0.075 mm (No. 200 Sieve). The sand used is from the Goksu River from Adiyaman, Turkey, the largest being 4.75 mm in size. The specific gravities of saturated dry surface for sand and crumb rubber are 2.73 and 1.05 g/cm3, respectively. The grading of the sand and crumb rubber is shown in Fig. 1. The Portland
The physico-mechanical behaviours of the samples
The object of physico-mechanical tests to examine whether the samples satisfy with requirements of relevant international standards for using in constructual applications. The results obtained from corresponding test series are first presented in Fig. 4 to illustrate the whole picture about the samples. The dimensionless ratios of parameters as a function of crumb rubber percentage are plotted. Dimensionless values are obtained by selecting maximum value of corresponding parameter as a scaling
Concluding remarks
The physico-mechanical and thermal properties of rubber-added bricks are investigated here. Various volumetric percentages of crumb rubber are replaced with conventional sand aggregates to form the brick samples. Seven different rubberized brick samples with varying crumb rubber percentages from 10% to 70% with 10% increments are compared with a conventional brick (control sample). The better and smoother surface is obtained. The observations during the tests show that the rubberized brick
Acknowledgement
The authors greatly appreciate The Turkish Scientific and Technical Research Institute for the fund provided for the present investigation (under grant TUBITAK-MAG-105M021).
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