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Concrete structures are designed with a specific service life in mind and deteriorate over time due to their exposure to environmental conditions. In order to increase the service life of concrete structures, they can sometimes be rehabilitated and repaired using concrete overlays. However, problems may develop between the new and old concrete due to differential shrinkage between the concrete substrate and overlay. These differential shrinkages typically result in the build - up of tensile stresses within the overlay. If the concrete does not possess sufficient tensile strength, the overlay will crack and or delaminate, which is usually considered failure. To prevent cracking, the quantity of shrinkage that occurs in the overlay needs to be minimised. Literature suggests that the addition of superabsorbent polymers (SAP's) to the concrete overlay can reduce the total shrinkage that occurs. A large amount of research exists pertaining to the use on SAP's in high performance concrete (HPC), while very little research has been done regarding their influence of overlays. This research investigated how the addition of SAP's to overlays containing silica fume (SF) would improve bonded concrete overlay performance. Testing was conducted on overlay samples with a water:binder (W/b) ratio of 0.45 and 0.55 with SAP contents of containing 0%, 0.2%, 0.4% and 0.6% of the total binder content. Samples were subjected to a large number of tests including compressive, tensile and shear bond strength, durability, tensile relaxation, elastic modulus, carbonation, bulk diffusion and free and restrained shrinkage. The results of this research indicate d that the SAP's had a greater influence on samples with a higher w/b ratio. The results also suggested that an increase in SAP content resulted in improved tensile strength, tensile relaxation and durability while also reducing the rate of drying shrinkage at early ages.
This is the state-of-the-art report prepared by the RILEM TC “Application of Super Absorbent Polymers (SAP) in concrete construction”. It gives a comprehensive overview of the properties of SAP, specific water absorption and desorption behaviour of SAP in fresh and hardening concrete, effects of the SAP addition on rheological properties of fresh concrete, changes of cement paste microstructure and mechanical properties of concrete. Furthermore, the key advantages of using SAP are described in detail: the ability of this material to act as an internal curing agent to mitigate autogenous shrinkage of high-performance concrete, the possibility to use SAP as an alternative to air-entrainment agents in order to increase the frost resistance of concrete, and finally, the benefit of steering the rheology of fresh cement-based materials. The final chapter describes the first existing and numerous prospective applications for this new concrete additive.
The purpose of this thesis is to investigate the ability of internal curing methods including superabsorbent polymers (SAP) and saturated lightweight aggregate to mitigate autogenous shrinkage and restrained shrinkage. This thesis also examines the changes in properties of concrete and mortar, such as permeability, when SAP, lightweight aggregate or shrinkage reducing admixtures (SRA) are introduced to the mix. This research found that mortar containing SAP was able to minimize the amount of autogenous shrinkage, but reduced the compressive strength considerably, similar to air-entraining concrete. SAP was also able to leave voids in the concrete, which simulate normal entrained air. SRA was most effective at reducing drying shrinkage. Lightweight aggregate has an interlocking bond with the paste at the interfacial transition zone; thus incresed its tensile strength properties.
Concrete curing is closely related to cement hydration, microstructure development, and concrete performance. Application of a liquid membrane-forming curing compound is among the most widely used curing methods for concrete pavements and bridge decks. Curing compounds are economical, easy to apply, and maintenance free. However, limited research has been done to investigate the effectiveness of different curing compounds and their application technologies. No reliable standard testing method is available to evaluate the effectiveness of curing, especially of the field concrete curing. The present research investigates the effects of curing compound materials and application technologies on concrete properties, especially on the properties of surface concrete. This report presents a literature review of curing technology, with an emphasis on curing compounds, and the experimental results from the first part of this research-lab investigation. In the lab investigation, three curing compounds were selected and applied to mortar specimens at three different times after casting. Two application methods, single- and double-layer applications, were employed. Moisture content, conductivity, sorptivity, and degree of hydration were measured at different depths of the specimens. Flexural and compressive strength of the specimens were also tested. Statistical analysis was conducted to examine the relationships between these material properties. The research results indicate that application of a curing compound significantly increased moisture content and degree of cement hydration and reduced sorptivity of the near-surface-area concrete. For given concrete materials and mix proportions, optimal application time of curing compounds depended primarily upon the weather condition. If a sufficient amount of a high-efficiency-index curing compound was uniformly applied, no double-layer application was necessary. Among all test methods applied, the sorptivity test is the most sensitive one to provide good indication for the subtle changes in microstructure of the near-surface-area concrete caused by different curing materials and application methods. Sorptivity measurement has a close relation with moisture content and degree of hydration. The research results have established a baseline for and provided insight into the further development of testing procedures for evaluation of curing compounds in field. Recommendations are provided for further field study.
The purpose of this thesis is to investigate the ability of internal curing methods including superabsorbent polymers (SAP) and saturated lightweight aggregate to mitigate autogenous shrinkage and restrained shrinkage. This thesis also examines the changes in properties of concrete and mortar, such as permeability, when SAP, lightweight aggregate or shrinkage reducing admixtures (SRA) are introduced to the mix. This research found that mortar containing SAP was able to minimize the amount of autogenous shrinkage, but reduced the compressive strength considerably, similar to air-entraining concrete. SAP was also able to leave voids in the concrete, which simulate normal entrained air. SRA was most effective at reducing drying shrinkage. Lightweight aggregate has an interlocking bond with the paste at the interfacial transition zone; thus increased its tensile strength properties.
Accurate correlation between standard test results and observed field performance of repair mortars has been difficult to achieve. A study was conducted in an attempt to understand the development of physical properties and induced tensile stresses as a repair material cures and how these affect the likelihood of early age cracking. A mathematical model was developed to predict when induced stresses may be sufficient to crack a repair mortar while curing. Using this technique, the influence of two polymers on a generic mortar was investigated in the laboratory. The laboratory study included measurements over time of tensile strength, drying shrinkage, tensile modulus of elasticity, and tensile creep. The model's predictions were checked by placing the studied mortars in a simulated repair situation.
The use of internal curing and specifically the use of super absorbent polymers has recently become an important topic in concrete research. Internal curing has been shown to reduce autogenous shrinkage in concrete mixtures, especially in high-strength mixtures where the water to cement ratio is low. Super absorbent polymer has not been studied in regards to its effect on pervious concrete. This research was conducted to examine the effectiveness of a commercially available super absorbent polymer in both standard and pervious concrete. The testing was initially conducted on mortar mixtures, followed by standard and high-strength concrete mixtures, and finally pervious concrete mixtures. Several tests were conducted including compressive strength, autogenous and total shrinkage, restrained shrinkage, moisture loss, abrasion, as well as others. The results followed similar trends as much of the previous research conducted on standard and high-strength mixtures containing super absorbent polymer. The pervious concrete containing super absorbent polymer showed an improvement in compressive strength, abrasion resistance, moisture loss, and total shrinkage compared to a control pervious mixture. If long term testing shows an improvement in the durability of pervious concrete containing super absorbent polymer, the applications for pervious concrete could be significantly increased.
The use of internal curing and specifically the use of super absorbent polymers has recently become an important topic in concrete research. Internal curing has been shown to reduce autogenous shrinkage in concrete mixtures, especially in high-strength mixtures where the water to cement ratio is low. Super absorbent polymer has not been studied in regards to its effect on pervious concrete. This research was conducted to examine the effectiveness of a commercially available super absorbent polymer in both standard and pervious concrete. The testing was initially conducted on mortar mixtures, followed by standard and high-strength concrete mixtures, and finally pervious concrete mixtures. Several tests were conducted including compressive strength, autogenous and total shrinkage, restrained shrinkage, moisture loss, abrasion, as well as others.