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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.

The use of plant ash as a sustainable cementitious material in concrete composition is a widely researched subject in the construction domain. A plant studied so far more for its thermal insulation properties, sunflower, was analyzed in this study with regard to its ash effects on the concrete composition. The present research aimed to analyze the effects of a 2.5%, 5%, 7.5%, 10%, 15%, 20%, or 30% volume replacement of cement by sunflower stalk ash (SA), a sustainable cementitious material, on the concrete compressive strength at 28 days and three months, the flexural and splitting tensile strengths, the resistance to repeated freeze–thaw cycles, and the resistance to chemical attack of hydrochloric acid. The elementary chemical composition of the SA and the composites was included also. According to the experimental results, SA decreased the values of the compressive and tensile strength of the concrete, but it improved the concrete behavior under repeated freeze–thaw cycles and under the action of hydrochloric acid. A percent of 10% of SA led to a much more pronounced development of compressive strength over time than conventional concrete (26.6% versus 12%).

Concrete, the most common material in the building industry, involves the use of mineral aggregates that represent an exhaustible resource, despite their large availability. For a series of applications, these mineral aggregates can be replaced by vegetal ones, which represent an easy renewable natural resource. In this study, two types of vegetal raw materials, namely sunflower stalks and corn cobs, were used in developing 10 compositions of ecological microconcrete, with different percentages involved: 20%, 35%, 50%, 65% and 80%, they were analyzed from the perspectives of density, compressive strength, splitting tensile strength, resistance to repeated freeze-thaw cycles, modulus of elasticity and thermal conductivity. The results revealed that the microconcretes with sunflower stalks registered slightly higher densities and better results regarding the compressive strength, splitting tensile strength, modulus of elasticity, and freeze-thaw resistance than those with corn cobs. Lightweight concrete is obtained when more than 50% replacement rates of the mineral aggregates are used.

In an increasingly urbanized world, construction industry is called upon to serve the needs of human society, such as environmental protection and safety in terms of infrastructure. In this context, a sustainable and ethical development means a close connection between buildings and environment. This connection can be achieved through, for example, the concept of ecological concrete or green concrete, as it is often called. The conventional process of obtaining cement and mineral aggregates from the concrete composition generates pollution, especially through greenhouse gas emissions. Also, one should not ignore the fact that extraction of the raw materials affects the habitats of the sites and of the neighboring areas. When construction materials are questioned, the ethical issues lay not in the means of expression, but mainly in the means of production. More to the point, the present contribution aimed to find solutions for enhancing the adhesion of vegetal aggregates with the cement matrix, in order to obtain a material with optimal mechanical properties, which is valued as an ethical approach of building industry. Results showed that plant aggregates can be used to obtain a building material which can be improved by using partial substitution of cement by silica fume, fly ash, or by using additives (sodium silicate and air entraining additive) and that green concrete as an environmentally friendly material offers the alternative for lower energy use and fewer CO2 emissions. Marketers must understand not only the advantages of these green materials, but also that they have an ethical commitment to provide consumers with environmentally friendly materials.

In the last few years, the building industry experienced a significant development as a response to the demographic growth of human society and to the increasing demand for housing. Their construction involves the traditional use of concrete as a material that provides added strength to the finished building. This is manufactured respecting standard recipes depending on the way of its use. Anyway, all concrete recipes involve the use of mineral aggregates extracted from the riverbed, as is happening in Romania, or rock blocks crushing, as reported in other countries. Under these conditions, the rationalization of the use of natural mineral resources and the identification of new possibilities to reduce their consumption through their replacement with vegetal waste has become an important research issue. In this study, two types of vegetal waste&mdash, namely, shredded corn cobs and sunflower stalks&mdash, were used to manufacture novel ecological concretes. The vegetal wastes, both in untreated and treated forms (with 20% and 40% of sodium silicate solution), were used to replace 50% of the river (mineral) aggregate volume. The obtained concretes were tested, and the values of some important parameters in the concrete characterization (such as bulk density, water adsorption capacity, compressive strength and splitting tensile strength) were compared with the concrete contains cement CEM II/A-LL 42.5R. The obtained results show that these vegetal wastes have the potential to be used in the manufacturing of new ecological concrete. In addition, this alternative material meets the requirements for the sustainable and healthy development of the environment, offering low-polluting solutions in the context of an increasing demand for constructions.

In the context of an urban environment assaulted by noise from different sources, the possibility of using composite materials made of concrete and various materials considered as waste was investigated, for the purpose of using them in acoustic barriers. Five different types of sustainable concrete have been developed, incorporating polystyrene granules, polyethylene terephthalate granules, corn cob granules, shredded sunflower stalk and balls made of sheep wool. Two different thicknesses were adopted, of 40 mm and 80 mm. The influence of the material's thickness was investigated. For these materials, the acoustic absorption coefficient was determined, using Feng's modified procedure of the ISO 10534:1998 standard. The sound absorption coefficient's meaning suffers changes and its measured value can be considered the real one, smaller than the usual reported standard values. Each of the sustainable concrete has sound absorption coefficients higher than those of the conventional concrete. The results highlighted that these types of materials represent a sustainable solution for both waste and noise problems of our cities.

The effects of the fly ash and of the sunflower stalks and corn cobs within a cement-matrix composite were studied under the aspects of density, compressive strength, splitting tensile strength, elasticity modulus, and resistance to repeated freeze-thaw cycles. In the research were developed 20 recipes of cement-based composite, including the reference composite. Fly ash was used as partial cement replacement (10, 20 and 30% by volume), and the vegetal aggregates made by corn cobs and sunflower stalks as partial replacement of the mineral aggregates (25 and 50% by volume). The study results revealed that a lightweight composite can be obtained with 50% of vegetal aggregates, and the fly ash, no matter its percentage, enhanced the compressive strength and splitting tensile strength of the compositions with 50% of sunflower aggregates and the freeze-thaw resistance of all compositions with sunflower stalks.

The use of wastes in building materials is an interesting and necessary domain of research. In concrete different types of wastes can be used as aggregates, as replacement of cement or as filler. The paper presents the results of experimental researches made on eco-concretes that included scrap or powder of waste tires. Several variables were investigated including two types of concrete with cement or with polymer, prepared with different dosage of tire wastes: in the case of cement concrete, the tire scrap was added in dosages of 25%, 30%, 40% and 50%. In the case of polymer concrete the tire powder was added in dosages of 6.4%, 12.4%, 17%, 20% and 23%. The compressive strength on cubes, the tensile strength by bending and the split tensile strength were determined. The tire waste addition decreased the values of mechanical strengths. In the case of cement concrete the best results were obtained for the concrete with admixture and a content of scrap tires of 25%. In the case of polymer concrete the mix with 23% epoxy resin and 17% tires powder had shown the best results for compressive strength. In the case of tensile strengths the mixes with a reduced dosage of epoxy resin and tire powder had shown higher values.