Abstract
The process of concrete obtaining involves high energy consumption, significant amounts of depletable natural raw materials, and greenhouse gas emissions. A greening variant of concrete is the substitution of the mineral aggregates from its composition with vegetal aggregates made by sunflower stalks. These vegetal aggregates have advantages from health, environment protection, comfort, energy saving, thermal, and/or sound insulation points of view. The aim of this chapter is to present the results of a research on concrete with sunflower stalk aggregates by applying a method of pretreatment of plant aggregates, and then a method of modifying the cement matrix, one of accelerating the hydration reaction of cement, and then a combination of cement matrix modification in parallel with the cement hydration reaction acceleration.
TopIntroduction
Population growth, pollution caused by human activity, production processes of building materials, all are directly related to increasing the level of greenhouse gases, which determines the approach by research specialists to find alternative methods to build more sustainable, more environmentally friendly. Concrete is a material widely used in constructions, and its demand is constantly growing. A major disadvantage of this classic construction material is its highly polluting character due to its manufacturing process but also due to its components. The process of cement obtaining involves high energy consumption (36% of global energy consumption) (Global ABC/IEA/UNEP, 2020), significant amounts of depletable natural raw materials (1.5 tons of raw materials to obtain 1 ton of finished product) (Ali et al., 2015), and greenhouse gas emissions (39% of total global CO2 emissions (Global ABC/IEA/UNEP, 2020), about one ton of CO2 for every tonne of cement produced (Błaszczyński & Król, 2015), thereby causing global warming and climate change, this industry being one of the most important industries responsible for major greenhouse gas emissions worldwide. In addition, the manufacture of concrete involves the use of natural mineral aggregates, another category of depletable natural resources.
The greening variants of concrete researched so far include the cement substitution with various pozzolanic materials such as metakaolin, silica fume, fly ash (Walczak et al., 2015; Glazer et al., 2011; Sijakova-Ivanova et al., 2011; Badur & Chaudhary, 2008; Ignjatović et al., 2016; Sua-iam & Makul, 2015), which decrease the environmental pollution by reducing the cement amount produced on the one hand, and the limitation of waste from landfills, on the other hand (Huntzinger & Eatmon, 2009). Another greening option is the substitution of mineral aggregates in the concrete composition. It is a widespread natural resource, but it is also depletable and in some places non-existent. (Langer et al., 2004). The amount of mineral aggregates extraction in Europe, for example, is about 7 tons per citizen of the European Union, given a global demand of about 22 billion tons per year (Danielsen & Kuznetsova, 2016). The aggregate extraction industry is one of the most important mining industries in the world, producing about 16.5 billion tons annually (Langer et al., 2004).
In the direction of replacing the mineral aggregates in the concrete composition, a variant studied lately is represented by the use of aggregates of vegetal origin. They have advantages from several points of view: health, ecological character, comfort, energy saving, thermal and/or sound insulation (Amziane & Sonebi, 2016). Plant aggregates are raw materials whose processing relatively simple contributes to reducing pollution and environmental protection (Farias et al., 2017). They are obtained, in general, from agricultural waste. Concrete with agricultural waste has good thermal properties, examples of such waste being palm bark, coconut shell, corn cobs, sunflower stalks, rice husk.
Key Terms in this Chapter
Ecological Concrete: Concrete that contains unconventional raw materials that are eco-friendly or its production involves sustainable fuels or other processes with a reduced energy consumption than the usual; in general, the production of ecological concrete assumes smaller greenhouse gas emissions than the normal concrete.
Green Building Materials: Building materials that imply in their production, placing or maintenance, processes with low environmental impact.
Thermal Conductivity: The degree by which a material let the heat pass through it.
Lightweight Concrete: Concrete with a density between 800 and 2000 kg/m 3 , made entirely or partially with light aggregates.
Agro-Waste: It consists in general of lignocellulosic biomass and it is produced as a consequence of different agricultural processes; it includes farm waste, harvest waste and others.
Sunflower Stalk: That part of the sunflower plant grown above the soil till under the hat with the seeds; it does not include the leaves.
Mechanical Properties: Physical characteristics exhibited by a material when one or multiple forces are applied upon it.
Natural Fibers: Fibers that are the result of geological processes or they are parts of plants or animals.
Vegetal Aggregates: Raw material obtained by the processing of different plants that are included in the concrete as partial or total replacement of the sand and/or gravel from its composition.