1. Introduction
รูปร่าง
Corresponding author.
E-mail address: nivanka@gfos.hr (I. Netinger). 1 www.gfos.hr. 2
www.zag.si.
http://dx.doi.org/10.1016/j.conbuildmat.2014.12.073 0950-0618/ 2015 Elsevier Ltd. All rights reserved.
รูปร่างPervious concrete has been in use for more than 50 years, especially in the United States and Japan [1,2]. It contains a high amount of pores, with cement paste evenly distributed throughout its structure. The porosity of pervious concrete ranges between 11% and 35% [3–5], which gives it permeability, good drainage properties, and high noise absorption characteristics; however, the high porosity also reduces the concrete’s strength. The most important features of pervious concrete in its hardened state are reduced density, permeability of 0.2–1.2 cm/s and compressive strength of 3.5–28 MPa [4]. Compared to regular concrete, pervious concrete has the main advantages of preventing water from pooling on surfaces, positively affecting vegetation by supplying plants with water/rainwater and maintaining groundwater quality [6]. These advantages make pervious concrete appropriate for a wide range of applications including slope stabilization systems, alleys, parking lots [4] and light-traffic roads [7].
Pervious concrete is composed of a mixture of cement, water, and coarse aggregate, with or without a small amount of fine aggregate [2]. Since pore connectivity is essential to pervious concrete function, compaction is restricted [8] because it can result in a layer of cement paste at the bottom of the concrete structure that would negatively affect permeability.
Total porosity of pervious concrete is the sum of closed (isolated) porosity and open (connected) porosity, and it can be calculated by hydrostatic weighing. However, direct insight into porosity would be beneficial since permeability is influenced not only by the number of pores but also by their distribution and interconnectivity. X-ray microtomography has been used to characterize many different types of building materials, including stone, concrete, and lightweight aggregate, and it enables assessing the total porosity, phase distribution, voids, and cracks. If supported by suitable image analysis software, X-ray microtomography can yield quantified results about the structure, pores, and pore interconnectivity [9–12]. Ayda et al. [13] previously investigated pervious concrete by means of microtomography (among other techniques) and found that aggregate properties have the strongest effect on the mechanical properties of porous concrete because the coarse aggregates are very effective in forming the skeleton structure. Microtomography scans enabled the researchers to follow crack patterns and determine that they were influenced by the distinct porous structure. The cracks extended into locations based on the geometry of the skeleton structure, which was determined by the aggregate grading. In particular, when the aggregates were fine, the cracks developed through the cement paste; with a larger aggregate size, however, the cracks developed more frequently through the aggregate grain [13].
The current study aimed to evaluate the influence of the aggregate type as well as the size and size distribution of aggregates on the mechanical properties and the overall porosity of pervious concrete and its application in pavement structures. This study was also intended to determine the optimal mixture for pervious concrete to meet the requirements of Croatian legislation for pavements [14]. According to the General Technical Conditions for Roadwork [14], concrete for pavement is classified based on its 28-day compressive and flexural strengths. The required compressive strength for a very heavy traffic load is C 35/45, while flexural strength must be 5.0 MPa. For a heavy traffic load, the required compressive strength is C 30/37 and flexural strength is 4.5 MPa, while the required load compressive strength and flexural strength are C 25/30 and 4.0 MPa, respectively, for other traffic. To quantify
Table 1 Mixture compositions.
pore volume and pore connectivity, X-ray microtomography was used, and microstructural analysis was done using a scanning electron microscope to qualify those results.
As a part of this study, the possibility of using a waste material, steel slag, instead of dolomite aggregate in pervious concrete was investigated. The use of steel slag in pervious concrete helps reduce industrial waste landfills, benefits ecological consciousness, and increases cost effectiveness.