Environmental Implications of CO2 Absorption by Pervious Concrete Pavement in Urban Roads

Abstract

This research deals with a new material, made from conventional pervious concrete, but with the addition of two components in its mixture, calcium hydroxide (Ca(OH)2), to improve its carbon dioxide (CO2) absorption properties from the atmosphere, and Scrap Tyre Tubes (STT), a rubber waste from used tyres of vehicle (motorcycles and cars), which makes the new material lighter and contributes to urban sustainability by reusing industrial waste automotive. Conventional pervious concrete has a main property that benefits the environment, which is natural from its porous structure, which is the permeability of the urban pavement, which allows the drainage of rainwater from the urban pavement to the underground, contributing to the reduction of flooding in cities through the infiltration of water into the groundwater. This research sought to improve conventional pervious concrete through additives in its mix to create a new porous material, more efficient at sequestering CO2 from the atmosphere, lighter and reusing rubber waste from used tyres. The porosity of conventional pervious concrete makes this material ideal for carbon dioxide (CO2) sequestration due to the ease of CO2 penetration into its internal structure pore network, which interacts with cement and other additives, which by means of a chemical reaction called carbonation, absorbs CO2 from the atmosphere to form calcium carbonate (CaCO3) in its internal structure, which is an excellent environmental benefit for the materials used in the manufacture of urban pavements, as it makes the urban pavement contribute directly for air quality and for the control of pollution emanating from motor vehicles traveling on urban roads. In this investigation were performed laboratory tests of compressive strength and permeability, because these are the most important properties of conventional permeable concrete that make this building material a porous pavement that can be used on urban roadways, these properties are essential for the new pervious concrete material, were also CO2 volume monitoring in contact with specimens of conventional pervious concrete and specimens of new material, because this environmental benefit of CO2 absorption from the atmosphere is very important for the control of air quality in large metropolis, which have high levels of pollution that affect the life of urban citizens, causing respiratory diseases in old and children. In this research, 40 conventional pervious concrete were manufactured with limestone aggregate, to serve as a control group in the statistical analysis and 10 specimens of the new material of pervious concrete also were manufactured with proportions of 1:0.5:4 (cement:Ca(OH)2:pebble), factor water/cement (w/c) of 0.30, with 5% STT in mix, because the proportion of SST in the mix defines how much waste tyre waste can be reused in the manufacture of this new material. The STT is a non-biodegradable material that occupies a lot of urban space, so it harms the environment and the quality of life of the urban citizen, an alternative to reuse STT in the mix of new pervious concrete material is a very important sustainable solution to modern cities around the world due to the progressive annual increase of this waste tire rubber from automotive industries. In this research the results of the tests served to compare compression and permeability, as well as monitoring the absorption of CO2 from the atmosphere of the different groups. The results of the compressive strength and permeability tests and CO2 volume monitoring were analyzed statistically for normality and the t-Student test. This analysis showed that the improvement of environmental properties harms the physical properties of the new material with compressive strength of 1.25 MPa, permeability of 7.00 mm/s and 5% of STT in the mix of new material of the pervious concrete, however, this new permeable concrete material can be used in non-structural works, such as garden pavement, pedestrian sidewalks, finishes to beautify buildings and condominium facades, etc., due to the environmental benefits it produces and cannot be neglected.