Concrete Durability

In this study, the influence of nanosilica hydrosols and rice husk ash (RHA) on the compressive strength, chloride permeability, electrical resistivity and capillary absorption of single and binary blended mortars was investigated. Results showed that the incorporation of nanosilica improved mortar performance, while RHA did not have a significant influence and mainly attributed to lower strength and durability at early ages. It was found that the addition of RHA in mixes containing nanosilica, dramatically decreased compressive strength at ages of 3 and 7 days. However, binary mixtures displayed the best results for strength development and durability at ages of 28 and 90 days.

A study was conducted to determine the effect of different concrete properties and prestressing steel indentation types on development length and flexural capacity of pretensioned members. Wires and strands commonly used in the manufacturing of prestressed concrete railroad ties worldwide were selected for the study. Thirteen different 5.32-mm-diameter prestressing wire types and six different strands (four, seven-wire strands and two, three-wire strands) were used to cast prisms with a square cross section. The ratio of concrete to prestressed steel in the test prism’s cross section was representable of typical concrete railroad ties. Thus, geometrical and mechanical properties of test prisms were representative of actual ties in the railroad industry.
To understand the effect of concrete-release strengths and slumps on development length, all parameters were kept constant in the prisms except concrete-release strength and slump. To manufacture prisms with different release strengths, all four wires/strands were pulled and de-tensioned gradually when the concrete compressive strength reached 3500 (24.13 MPa), 4500 (31.03 MPa), and 6000 (41.37 MPa) psi. To determine the effect of different slumps on development length, prisms with different slumps of 3 in. (7.6 cm), 6 in. (15.2 cm), and 9 in. (22.9 cm) were manufactured and all other parameters were kept constant in prisms. All prisms were tested in three-point bending at different spans to obtain estimations of development length based on type of reinforcement, concrete-release strength, and concrete slump. Lastly, a design equation was developed based on experimental data for prediction of development length.
In the last phase of load tests, cyclic-loading tests were conducted on the prisms manufactured with wires to evaluate the bond performance of wires with different indentation types under cyclic loading.
A total of 210 load tests, including 14 cyclic tests, were conducted. The monotonic-load tests revealed a large difference in the development length of pretensioned concrete members manufactured with different wire/strand types and different concrete-release strengths. Also, the cyclic-load tests revealed a significant difference in bond performance of different wire types under cyclic loading compared to monotonic loading.

Abstract. This paper investigates the optimized performance of reactive powder concrete. The effect of binder content
and incorporation of steel fiber and/or quartz powder on fresh, mechanical and microstructure properties of RPC
specimens were studied. The resistance to chloride penetration was tested for some specimens.The results show that
the compressive and splitting tensile strength of RPC specimens enhanced as the binder content increased. Also, the
incorporation of steel fiber and/or quartz powder significantly improves the strength and chloride penetration
resistance properties.The effect of binder content, steel fiber and quartz powder on the microstructure of RPC was
explained using XRD and SEM analysis. Unhydrated cement phases and calcium silicate hydrate were indicated in
the XRD diffract grams. The SEM images showed the compact interfacial zones and limited small pores in specimens
with high binder content and incorporated with steel fiber and quartz powder.
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This review paper investigated the durability and corrosion of materials used in the construction of agricultural buildings. Even though concrete and metal were the materials of choice in the construction of farm structures, they are susceptible to corrosion and environmental degradation. Acid attacks result in the oxidation of metals and mass losses and reduced compressive strength of the metal structures. Concrete structures are degraded in high humidity environments, such as lagoons, agricultural effluents, and animal manure. Poultry, cow, and pig manure contain variable quantities of corrosion-inducing chemicals, such as sulfates, nitrates, chlorides, hydrogen sulfide, and ammonia. However, the degradation of concrete structures can be mitigated by the utilization of modified concrete containing sulfur, fly ash, silica fume, and nanoparticles such as silica. Concrete structures made of fiber-reinforced polymers are less prone to corrosion and are more durable. The design for dur...

Exposure conditions for accelerated testing of the resistance to PSA are evaluated. Mass loss was the most efficient method for the deterioration rate evaluation. The UPV and resonant frequency were not suitable for evaluation of PSA degradation. a b s t r a c t Sulfate attack can cause serious damage to concrete structures. Susceptibility of binders to chemical sul-fate attack is often tested, however, no standard method exists for evaluation of concrete's resistance to physical sulfate attack. Traditional field testing of concrete's resistance to sulfate attack may take several years. Thus development of an accelerated testing procedure is required. The aim of this research is to evaluate suitable exposure conditions and deterioration evaluation methods suitable for accelerated testing. A number of methods for assessment of the level of deterioration were assessed. It was found that 100 thermal cycles between 5 and 30 °C while immersed in 30 wt% sodium sulfate solution were sufficient to assess the resistance of a wide range of mortar mixes. The mass loss proved as the most effective measure of the deterioration level.

SCC is a highly flowable and non-segregating concrete that spreads into the form by means of its own weight. By adding more amount of finer material and by aiding super-plasticizer, the consistency of concrete may alter, resulting to materials of higher mass may tend to settle down. This paper investigates the workability of blended RHA and FA as 20% partial replacement to cement on SCC. SCC was made by usual ingredients such as cement, fine and coarse aggregates, water, FA, RHA, and 3% super-plasticizer. The experiment was carried out by adapting 0.30 w/cm ratio. Workability test determined its flowability and filling ability using slump flow test and U-Box Test. Moreover, the compressive strength of SCC was investigated at 3, 7, 14 and 28 curing period. The result shows that blended RHA and FA as 20% partial replacement to cement on SCC has better workability and compressive strength compared to the controlled mix.

ABSTRACT In this study, the influence of nanosilica hydrosols and rice husk ash (RHA) on the compressive strength, chloride permeability, electrical resistivity and capillary absorption of single and binary blended mortars was investigated. Results showed that the incorporation of nanosilica improved mortar performance, while RHA did not have a significant influence and mainly attributed to lower strength and durability at early ages. It was found that the addition of RHA in mixes containing nanosilica, dramatically decreased compressive strength at ages of 3 and 7 days. However, binary mixtures displayed the best results for strength development and durability at ages of 28 and 90 days.

The microstructure of the steel-concrete interface (SCI) in reinforced concrete is closely related to corrosion of reinforcing steel bars. Accordingly, characterization of the SCI is receiving increasing research attention. For microscopical observations of the SCI, a cutting process is needed to create a flat cross-section. Cutting carries the risk of damaging the SCI because of the considerable difference of hardness between concrete and steel. However, studies on characterizing the microstructure of the SCI rarely consider the damage induced by the potentially inappropriate cutting process. This study investigated the damage created by three cutting methods, namely, mechanical sawing, laser cutting, and combined laser-water cutting by the Laser MicroJet technology (LMJ). The SCI of the cut sections was imaged by scanning electron microscopy equipped with a backscattered electron detector. Additionally, the specimens were non-invasively studied by X-ray microtomography before and after cutting, to compare the impact of various cutting techniques on inducing damage to the SCI beneath the cutting surface. The results showed that if a bleed water zone (BWZ) is present, the cutting technique and protocol can significantly influence the morphology of this zone and adjacent regions. This study recommends an optimized mechanical sawing protocol with low feed speed as this led to considerably less SCI damage than laser and LMJ cutting. Moreover, it was found that adjusting the cutting direction can further significantly reduce the damage created during cutting. The least damage was found when the saw blade cut through the steel before cutting the BWZ. The main problem with laser cutting was heat generated even for a relatively low laser power; therefore, a heat-affected zone was created which significantly altered the microstructural features of the SCI not only on the cutting surface but also a certain depth below the surface. In LMJ cutting, this thermal effect was significantly reduced, however, the high-pressure water eroded the porous SCI and caused cracks. These effects can penetrate along the BWZ into the interior material. To complete this study, two applications demonstrate that the optimized mechanical sawing protocol is applicable to concrete specimens with rebars of actual size and corroded rebars.

The need for an accurate determination of the chloride threshold value for corrosion initiation in reinforced concrete has long been recognized. Numerous investigations and reports on this subject are available. However, the obtained chloride threshold values have always been, and still are, debatable. The main concern is linked to the methods for corrosion detection and chloride content determination in view of the critical chloride content itself. In order to measure the chloride content, relevant to the corrosion initiation on steel, destructive methods are used. These traditional methods are inaccurate, expensive, time consuming and noncontinuous. Therefore, the application of a cost-effective Ag/AgCl ion selective electrode (chloride sensor) to measure the chloride content directly and continuously is desirable. The advantage would be an in situ measurement, in depth of the concrete bulk, as well as at the steel/concrete interface.

This review paper investigated the durability and corrosion of materials used in the construction of agricultural buildings. Even though concrete and metal were the materials of choice in the construction of farm structures, they are susceptible to corrosion and environmental degradation. Acid attacks result in the oxidation of metals and mass losses and reduced compressive strength of the metal structures. Concrete structures are degraded in high humidity environments, such as lagoons, agricultural effluents, and animal manure. Poultry, cow, and pig manure contain variable quantities of corrosion-inducing chemicals, such as sulfates, nitrates, chlorides, hydrogen sulfide, and ammonia. However, the degradation of concrete structures can be mitigated by the utilization of modified concrete containing sulfur, fly ash, silica fume, and nanoparticles such as silica. Concrete structures made of fiber-reinforced polymers are less prone to corrosion and are more durable. The design for dur...

ABSTRACT In this study, the influence of nanosilica hydrosols and rice husk ash (RHA) on the compressive strength, chloride permeability, electrical resistivity and capillary absorption of single and binary blended mortars was investigated. Results showed that the incorporation of nanosilica improved mortar performance, while RHA did not have a significant influence and mainly attributed to lower strength and durability at early ages. It was found that the addition of RHA in mixes containing nanosilica, dramatically decreased compressive strength at ages of 3 and 7 days. However, binary mixtures displayed the best results for strength development and durability at ages of 28 and 90 days.

This review paper investigated the durability and corrosion of materials used in the construction of agricultural buildings. Even though concrete and metal were the materials of choice in the construction of farm structures, they are susceptible to corrosion and environmental degradation. Acid attacks result in the oxidation of metals and mass losses and reduced compressive strength of the metal structures. Concrete structures are degraded in high humidity environments, such as lagoons, agricultural effluents, and animal manure. Poultry, cow, and pig manure contain variable quantities of corrosion-inducing chemicals, such as sulfates, nitrates, chlorides, hydrogen sulfide, and ammonia. However, the degradation of concrete structures can be mitigated by the utilization of modified concrete containing sulfur, fly ash, silica fume, and nanoparticles such as silica. Concrete structures made of fiber-reinforced polymers are less prone to corrosion and are more durable. The design for durability has also emerged as a viable option for optimizing the service life of agricultural buildings by adhering to the exposure limits.

Although works have been carried out to explore the influence of adding micro silica (MS) and nano silica (NS) mixture on the main characteristics of cementious materials, the synergistic role of micro-nano silica mixture was rarely studied on the direct corrosion protection performance of concrete. This research is to investigate the efficiency of using MS and NS mixture, as cement partial replacement, on corrosion protection and sulphate resistance of cementious materials. In addition, the influence of this silica multi-sized mixture was also studied on some durability characteristics related to corrosion and sulphate pro-tection. Based on the maximum mortar compressive strength, 10% MS and 2% NS were the optimum cement replacement ratios for each size separately. For the comparative purposes, the total cement replacement ratio of MS and NS mixture was kept equal to the optimum MS (i.e.10%) and hence the optimum mixing ratios for combining MS and NS in a mixture were equal 8% and 2% respectively. Concrete corrosion protection and mortar sulphate resistance were remarkably enhanced by using 2%NS + 8%MS mixture, instead of the optimum MS or NS cement replacement ratios. Further sensitivity study is recommended for the proposed MS + NS mixture considering more controlling factors.

The efficiency of generic and proprietary corrosion inhibitors (based on nitrite, amine carboxylate or amino alcohol) in corrosion mitigation of carbon steel, which is exposed to concrete solutions with different amounts of chloride as well as sulfate, was studied. The corrosion protection provided by the selected corrosion inhibitors was investigated by performing a potentiodynamic polarization study. In addition, the surface morphological properties of carbon steel samples exposed to the electrolyte mixed with or without inhibitors was also evaluated by scanning electron microscopy. The potentiodynamic polarization measurements showed that the evaluated inhibitors decreased the corrosion current density by 1.6 to 6.7 times depending on the type of inhibitor and the level of sulfate concentration in the electrolyte. The performance of inhibitors based on nitrite was better than that of inhibitors based on amine carboxylate or amino alcohol. The possible mechanisms of the inhibition...