This research focuses on the effects of self-healing on the different transport properties of microcracked Engineered Cementitious Composites (ECC) with different maturity levels and incorporating three different mineral admixtures with greatly varying chemical compositions. The effect of self-healing capability on transport properties was assessed using water sorptivity and rapid chloride permeability tests (RCPT). Experimental results revealed that with the selection of proper mineral admixture type and conditioning, a 92% recovery in water sorptivity results is attainable. Moreover, a considerable amount of this recovery took place after only 7 days of water curing, significantly lowering the risk of water transport by capillary suction into cracked ECC. Like the sorptivity measurements, most of the chloride ion penetrability values could also be reduced up to a great extent after 30 days of water curing, so most of the results fell into the low penetrability level during this period, as prescribed by ASTM C1202. Although self-healing in terms of RCPT results started to be visible in the first 7 days of water curing, significant improvements needed more time in RCPTs, unlike the sorptivity results. Overall, these findings suggest that the rate of self-healing varies depending on the different transport mechanisms dominant in a given infrastructure type during its service life.
Once ice forms in highly saturated concrete material, internal tensile stress will be generated and causes damage to the material, which is a serious problem for concrete structures in cold and wet regions. On one hand, each component (porous body, ice and liquid) should satisfy the compatibility of stress and strain, which has been discussed by the poromechanical theories. On the other hand, if some empty voids exist, the hydraulic pressure will release when liquid water escapes from the expanded area according to Darcy's law. Recent closed freeze-thaw tests on the saturated mortar showed a consistent tendency: as the number of freeze-thaw cycles (FTC) increases, the deformation changes from the expansion to the contraction. In order to make clear the physical and mechanical changes during this process, a more comprehensive hydraulic model is developed, which combines both the mechanisms mentioned above. The estimated strain behavior by this model is in a good agreement with experimental measurements, and also, it has good potential and is more flexible to be applied to different cases such as different saturation degrees and cooling rates. The permeability change can be also considered in this model as a reflection of frost damage level.
The tensile behavior of plain round reinforcing bars corroded with various radius losses along their length is investigated experimentally and analytically. In the experiments, various corrosion topographies are simulated through accelerated electric corrosion tests using bare rebar specimens and different cathode arrangements. The tensile performance of the corroded specimens is then studied using a digital image processing method, showing that tensile degradation resulting from corrosion is closely related to radius loss variability. For the analysis, a numerical model based on the rigid body spring method incorporated with a truss network is proposed for the evaluation of tensile behavior in consideration of radius loss. Good agreement with the test data is obtained with the proposed model, which offers an accurate method of estimating the residual tensile capacity of corroded rebars.
Production of cement is ranking 3rd in causes of man-made carbon dioxide emissions world-wide. Thus, in order to make concrete more sustainable one may work along one or more of the following routes; 1) Replacing cement in concrete with larger amounts of supplementary cementing materials (SCMs) than usual, 2) Replacing cement in concrete with combinations of SCMs leading to synergic reactions enhancing strength, 3) Producing leaner concrete with less cement per cubic meter utilizing plasticizers and 4) Making concrete with local aggregate susceptible to alkali silica reaction (ASR) by using cement replacements, thus avoiding long transport of non-reactive aggregate.
Available experimental studies on the effect of the interfacial transition zone (ITZ) on transport properties of cement-based composite materials appear to be ambiguous. The main objective of this work was to enhance the understanding of the relationship between ITZ and transport properties of Portland cement-based materials by using both a rapid chloride migration test and theoretical calculations. A densification factor which is related to aggregate volume content was introduced to further determine the transport properties of ITZ. Results indicate that the overall porosity decreased with increasing aggregate volume content due to the dilution effect by impermeable aggregates. The porosity was above the theoretical dilution line obtained from P0×(1-Vagg) for mortars with more than 20% of aggregate, which can be attributed to the presence of high porous ITZ. On the other hand, more porous ITZ was expected to be accompanied by a denser bulk cement matrix, which leaded to a decrease in the porosity of mortar with less than 35% of aggregate. The ITZ effect would dominate the blocking aggregate, densification and tortuosity of bulk paste when aggregate volume content exceeded 0.35. The ratio between the migration coefficient of the ITZ and that of the matrix (DITZ/Dmatrix) increased with aggregate volume content and assumed ITZ thickness. In addition, the influence of ITZ increased with increasing the degree of interconnection slightly until 1.0. Beyond this value, a sudden increase in DITZ/Dmatrix ratio was observed indicating the negative percolation effect when the adjacent ITZ start to interconnect.
The purpose of this paper is to propose a material design method of lightweight cement-based composites that reduces the mass of building components and provides them with better insulation. To achieve this purpose, a number of special lightweight aggregates were tested. Furthermore, material design methods based on the packing density models and the void system model for lightweight porous mortar (LWPM) were applied. A series of experiments was carried out in order to investigate the mechanical properties and to examine the thermal conductivity of various types of lightweight mortar. The study identified that the adopted material design methods were effective in reducing the density of lightweight mortar and in obtaining sufficient insulation performance. Furthermore, compressive strength sufficient for required structural performance was also achieved in certain types of lightweight mortar. Finally, lightweight insulation block (LWIB) was developed by combining the packing density model and the void system model for achieving both of sufficient bearing capacity and high insulation performance.
The feasibility of using layered- Functionally Graded Self Compacting Cement Composite (FGSCCC) for precast shield-tunnel segments, in harmony with present concrete industry sustainability trend, is presented herein. Limestone powder-type Self-Compacting Cement Composites (SCCC) either with silica fume (SiF) or with SiF and steel fibres (SF) were formulated for the watertight layer. While, SCCC with polypropylene fibres (PPF) or light weight aggregates and SF (LWA+SF) were used for the fire-resistant ones. Besides, a high strength SCCC (HS-SCCC) was considered for structural layers and monolithic samples. Layer composition influence and interlayer robustness on the structural element properties were evaluated. Experiments showed that the FGSCCCs are more effective than the HS-SCCC solu-tions in front of water, chloride, carbonation, fire or in terms of residual strength. Thanks to its precise spatial material arrangement, the effect of fire or the risk of steel reinforcement corrosion substantially decreases. The residual compressive strength, of FGSCCC specimens with LWA+SF layers, slightly decreases compared to that with PPF layers. Furthermore, they showed the increase of toughness of these specimens. Although none sharp failure at interface was observed, the results pointed out the necessity of considering other different effective parameters for validating the significance of casting process based on rheology.
This paper presents an approach to assess environmental impacts in terms of CO2 resulting from applying combined repairs to extend service life of marine concrete structures. The service life is defined by considering chloride ion diffusion using the partial differential equation of the Fick’s second law. However, the equation cannot simply be solved, when the concrete structures are repaired with three strategies, i.e., concrete cover replacement, silane treatment, or combinations of them. The difficulty deals with solving nonlinear chloride ion concentration profile and space-dependent diffusion coefficient after repairs. To remedy the difficulty, the finite difference method is used. By numerical computation, nonlinear chloride ion concentration profile can be treated point-wise. Based on the Crank-Nicolson scheme, a formulation for space-dependent diffusion coefficient can be derived. Using the aforementioned idea, space- and time-dependent chloride ion concentration profiles can be presented, and the extended service life of concrete structures after repairs can be computed. In repairs for extending the service life, the CO2 occurs due to repair material production and repair processing of three repair strategies. For comparing the performance of those strategies, the CO2 and cost are considered with the service life extension. Numerical examples and observation are finally presented.
There has been no such engineering method until now to enable water curing in the vertical surfaces of concrete after the removal of formworks. The Aqua curtain wet curing system has been developed with the purpose of supplying the sufficient water on vertical surfaces of concrete. Aqua curtain prevents rusting of reinforcing bars by making the surface of concrete denser. In this way, Aqua Curtain also contributes to realize more resistant and long-life concrete structures. In other words, implementation of this system leads to improve the endurance and economy of concrete structures by reducing the consumption of resources.
The effects of porous concrete on water quality improvement in artificial sewage water were examined in the laboratory test. In-situ test using water channel confirmed the purifying function of precast porous concrete products on water quality. Purification practice to improve water quality of an urban river was conducted by placing precast porous concrete products in the river. For the porous concrete used in the tests, two different sizes of coarse aggregate of 5~10, 10~15 mm were used. Three void contents of 20, 25 and 30 percent were designed for the porous concrete. Variation of water quality was observed by the indexes of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), total phosphorus (T-P) and total nitrogen (T-N) in the laboratory test and in-situ test. It was found that during the period of 70~170 days since the experiment started, void content of porous concrete did not influence the purifying ratio of TOC in sewage, while the purifying ratio of TOC in laboratory by porous concrete changed to around 60 to 80 percent. The purifying ratio of T-P in laboratory was about 20~40 percent, whereas river water purification test showed a higher purifying ratio of T-P. It was found that BOD, COD of the river water decreased about 30 to 60 percent by placing porous concrete products in the river.
This paper reports on an experimental program investigating the durability and mechanical properties of alkali activated slag concrete (AASC). The AASC was prepared using ground granulated blast furnace slag activated by high concentration alkali solution. The mechanical properties were determined by compressive strength and elastic modulus. The durability characteristics of AASC were measured using Ultrasonic Pulse Velocity (UPV) and permeable voids tests. The result showed that AASC developed a comparable strength to Portland Cement (PC) concrete over the short term. However, the material displayed an increase in voids, as well as a reduction of velocity over time. This could lead to the material displaying inferior performance over longer periods of time.
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