The primary aim of this paper is to study the effect of key mix parameters on tortuosity and permeability of concrete' s pore system, the two important material properties related to concrete durability. The measurement of tortuosity requires determination of porosity and pore size of concrete. Eighteen different concrete mixes were prepared by varying the levels of the key mix parameters, namely water/cement ratio, cement content and coarse/fine aggregate ratio, and then tested to determine porosity, pore size, tortuosity, and permeability. The experimental data were used to study the effect of the key mix parameters on porosity, tortuosity and permeability of concrete. While all the selected parameters of mix design have some influence on tortuosity of the pore system and permeability, the most dominant one is the water/cement ratio, which can be rated as the single most significant parameter. Test data also show that permeability decreases with increasing tortuosity, but the decrease is marginal with tortuosity of the pore system exceeding a value of 150.
This paper presents a new classification system called the Marine Structure Health index (MSHi). An evaluation model based on the fuzzy Delphi analytic hierarchy process (FDAHP) has been used for estimation of health in marine concrete structures. For this purpose, fifteen types of cracking in concrete, surface distresses, and miscellaneous distresses have initially been investigated and rated. In the MSHi system, a number from 0 to 100 is assigned to the health of a structure. Based on the MSHi classification, the health of a structure is classified into five modes from the view point of distress: very poor, poor, medium, good and very good.
Most of the previous research on the use of recycled materials for concrete examined only the effect of using recycled aggregate in concrete mixes. In this paper, the combined effects of recycled aggregate and recycled water on the strength and durability of recycled concrete are presented and discussed. Three types of mixing water were examined and found to comply with the requirements of EN 1008 and ASTM C94. The test program involved the preparation of a moderate strength concrete made out of recycled water and recycled aggregate obtained from demolition and construction wastes. In the demolition waste series, four mixes of concrete were prepared using different contents of aggregate extracted from demolition waste and recycled water. The effect of the recycled aggregate and recycled water on the axial and flexural strength was found to be moderate but had a significant negative impact on the durability. In the construction waste series, to enhance the durability and to lower the carbon footprint of the recycled concrete mix, the OPC was replaced by GGBS. Four replacement ratios, 60%, 70%, 80%, and 90%, of the OPC were examined. While all the four mixes achieved good strength and durability, the mix with 90% GGBS did not achieve the target strength of 40 MPa even after 56 days. In general, fully recycled concrete mix with 80% GGBS replacement is recommended for any sustainable future construction in the Gulf with an expected carbon footprint of 129.9 kg/m3.
This paper proposes an innovative strain energy frame impact machine (SEFIM) designed to explore direct tensile behavior of high performance fiber reinforced cementitious composites (HPFRCC) at high strain rates. The proposed system utilizes an energy frame to store a large amount of elastic strain energy as well as to suddenly generate high rate tensile impact pulse. The prototype of SEFIM demonstrated that the proposed energy frame could store enough elastic strain energy to fail a large-sized tensile specimen at high strain rates in direct tension. The tensile stress versus strain curve of HPFRCC under high rate impact was obtained by using the prototype with the aid of a high speed camera system and dynamic strain gauges attached on the surfaces of the transmitter bar.