Kosmas K. Sideris

Concrete is the most used construction material worldwide and material with the second greater consumption globally, just after water. However, durability of concrete is a major problem that minimizes the service life of structures. Concrete deterioration is almost always caused by reactants that penetrate the concrete matrix with water. Therefore, almost all concrete structures require protection from water. One of the most effective ways to protect concrete from the ingress of water for a lifetime interval is the use of crystalline admixtures. Their effectiveness in watertight concrete is well proven in several projects around the world. However, their influence on the long-term durability of concrete under different durability environments is not well understood. A long-term experimental program was carried out at the Building Materials Laboratory (BML) at Democritus University of Thrace to investigate the effect of crystalline admixtures in prolonging the service life of concretes. A total of 12 concrete mixtures were produced and crystalline admixtures were added in six of them. All specimens were used for the estimation of the carbonation resistance factor and the chloride migration coefficients according to the relevant European standards. These indicators were used to calculate service life of all mixtures. Results indicate that addition of crystalline admixtures enhances durability of concrete mixtures and prolongs the service life of reinforced concrete structures up to 80%.

Τhe aim of this work is to verify the increase in durability of concrete after the application of an external waterproofing system with crystalline technology. More specifically, two water tanks were cast with two different classes of concrete. These tanks were then filled with water. External waterproofing crystalline system was applied with a surface coating on one of the four sides of each tank. After the completion of eight months from the application of the system, core samples were taken from each tank from the sides where the material had been applied as well as from those that remained intact. These samples after appropriate preparation were subjected to chloride resistance, carbonation and water absorption tests according to European standards. From the results of the conducted tests and the comparison between them, for each tank, safe conclusions about the durability of the concrete were drawn. It was concluded that the application of the external waterproofing system with crystalline technology increased the durability indicators in both concrete tanks. These resulted to the increase of the service life of the concrete sealed with the specific material

Self-compacting concrete (SCC) is a high-quality construction solution, combining high fluidity, passing and filling ability with improved mechanical properties and durability. In the present study, the effect of incorporating alternative waste materials, such as two by-products of the cement industry, namely cement kiln dust (CKD) and by-pass dust (BPD) into SCC, as a partial replacement for traditional filler material, was investigated. The produced compositions were compared with reference mixtures containing exclusively marble powder (MP), as a filler. A series of tests encompassing specific test methods for wet SCC, compressive, flexural and tensile-splitting strength tests, as well as drying-shrinkage determination, were undertaken to evaluate the quality of the produced SCC in terms of fresh and hardened properties. The use of alternative fine-filler materials resulted in a high-performance sustainable SCC, of low cement content. To be precise, incorporating CKD into the SCC enhanced its rheological behavior and marginally improved its mechanical properties, while the use of BPD led to SCC mixtures of adequate rheological characteristics, coupled with significantly improved mechanical and physical properties.

Self-compacting concrete (SCC) is a high-quality construction solution combining high fluidity, passing and filling ability with improved mechanical properties and durability. In the present study, the effect of incorporating alternative waste materials, such as two by-products of the ce-ment industry, namely cement kiln dust (CKD) and by-pass dust (BPD), into SCC as partial re-placement for traditional filler material was investigated. The produced compositions were compared with reference mixtures containing only marble powder (MP) as a filler. A series of tests including specific test methods for wet SCC, compressive, flexural and tensile splitting strength tests as well as drying shrinkage determination were conducted to evaluate the quality of the produced SCC in terms of fresh and hardened SCC properties. The use of alternative fine filler materials resulted in a high-performance sustainable SCC of low cement content. Specifi-cally, incorporating CKD into the SCC enhanced its rheological behavior and improved slightly its mechanical properties, while the use of BPD led to SCC mixtures of adequate rheological characteristics but with highly upgraded mechanical and physical properties