Nowadays green buildings are a necessary component of securing sustainability, whereas concrete composites with the addition of siliceous fly ash (FA) can certainly be included in the sustainable and green concrete. Effective promotion of green concrete incorporating FA is required in order to minimize the environment threat due to FA waste disposal and reduce cement consumption. In this paper, effects of FA addition on the compressive strength and fracture toughness of cm f plain concrete are presented. Fracture toughness tests were carried out according to Mode I (tension at bending) following the RILEM Draft Recommendations. The critical values of stress intensity factors, have been determined. S KIc To assess mechanics parameters compressive strength tests and fracture toughness tests were conducted and the results were evaluated comparing with reference concrete. In modified concretes, cement was replaced by FA by its weight. Three test groups were constituted with the replacement percentages as: 0% (FA-00), 20% (FA-20) and 30% (FA-30). During the tests, the effect of age of concretes modified with the additive of FA on analysed parameters was determined. The experiments were carried out after: 3, 7, 28, 90, 180 and 365 days of curing. Based on the obtained results it can be concluded that, it is possible to make green concrete containing FA with high compressive strength and fracture toughness. The properties of composites with the additive of FA depend on the age of the concrete during tests. 20% additive of FA guarantees high and in mature concretes. Moreover results of the and cm f S KIc S KIc the are convergent qualitatively.

Introduction

Nowadays, principles of sustained development and ecology are an important issue in design of concrete compositions. Furthermore, the conservation of resources and environment for a sustainable future has been today’s one of the biggest challenges (Gursel et. al., 2016). Changes resulting from more and more frequent use of hybrid cements in the concrete technology based on mineral additives, which are by-products of other industrial or agricultural processes, have a beneficial effect on not only the reduction of CO2 emission but also constitute the basis of the so-called sustainable – green concrete concept (Aitcin, 2000; Meyer, 2009; Yang et. al., 2016). Structures made of green concrete are environmentally sustainable and are constructed in such a way that the total impact on the environment during their full life cycle, including service life, is reduced to a minimum. In this context, responsible green construction should be energy efficient and made of environmentally friendly materials. Concrete used in such structures must meet the requirements for strength and durability and its components should be obtained, produced and used in an environmentally friendly manner (Aitcin, 2000; Jayapalan and Lee, 2013). Furthermore, green buildings are a necessary component of securing sustainability. According to Thatcher and Milner (2016) health, wellbeing, and effectiveness in green buildings is an important motivator for their occupants. Interesting proposal and suggestions for designing more sustainable and greener concrete were proposed by Long et. al. (2015). It should be noted that in the last several dozen years, with the development of a new generation of composites, i.e. green concrete composites, significantly increased the production of concrete mixtures containing different types of supplementary cementitious materials (SCMs) (Lothenbach et. al., 2011).