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Bleeding can be described as water coming out from fresh cement paste, which not only affects the homogeneity at fresh stage but also decides the hardened state structure. Previous studies have focused on the determination or simulation of the bleeding extent of fresh cement paste and give objective conclusions. However, there are rare researches about the influence of bleeding on the final structure of cement paste. In this study we have monitored the cement paste with various bleeding caused by water cement ratio and slag replacement. The microstructure development of cement paste from top to bottom was measured by using lowfield NMR with Hahn spin sequence from 6 h to 72 h. Results showed that within 4.4 mm bleeding thickness the bleeding will decrease the slope of the void ratio as a function of distance which suggests a homogeneous structure is formed. However, when the bleeding water thickness is higher than 4.4 mm, hydration would lead to a heterogeneous structure. Detailed discussions on the connection between the bleeding and the final structure are also presented in this paper.

Bleeding can be described as water coming out from fresh cement paste, which not only affects the homogeneity at fresh stage but also decides the hardened state structure. Previous studies have focused on the determination or simulation of the bleeding extent of fresh cement paste and give objective conclusions. However, there are rare researches about the influence of bleeding on the final structure of cement paste. In this study we have monitored the cement paste with various bleeding caused by water cement ratio and slag replacement. The microstructure development of cement paste from top to bottom was measured by using lowfield NMR with Hahn spin sequence from 6 h to 72 h. Results showed that within 4.4 mm bleeding thickness the bleeding will decrease the slope of the void ratio as a function of distance which suggests a homogeneous structure is formed. However, when the bleeding water thickness is higher than 4.4 mm, hydration would lead to a heterogeneous structure. Detailed discussions on the connection between the bleeding and the final structure are also presented in this paper.

As an internal curing material, superabsorbent polymers (SAPs) can effectively reduce the risk of volume shrinkage of cement-based materials. By preparing the cement paste mixed with SAPs, the amount of pre-absorbed water and the water-cement ratio of paste on the water absorption-release behavior in the fresh cement paste were studied by using 1H low-field NMR. The results showed that when the water-cement ratio was 0.30, the SAPs without pre-absorption could absorb the mixing water from the fresh paste and stored the mixing water in the SAPs relatively stable, while the pre-absorbed SAPs released the absorbed water into the paste rapidly, and the more pre-absorbed water, the faster the water released after mixing. When the watercement ratio was increased to 0.40, the mixing water absorbed by SAPs without pre-absorption was more than that absorbed by SAPs when the water-cement ratio was 0.30, but in the system with super high water-cement ratio of 0.50, the SAPs cannot absorb mixing water from the paste after mixing.

With freshwater getting scares seawater, i.e., water containing NaCl, can become the only viable option for making concrete. Although a lot of research had been directed to understanding the role of water in cement hydration, not much is known about the interaction of the Na+ and Cl- with cement paste during drying. A problem is that available techniques like, i.e., XRD, SEM, and EDX, for measuring the microstructure and the methods for determining the concentration of Na+, Cl- ions in pore solutions are either indirect or invasive and moreover often destructive, which consequently may lead to inadequate interpretations. Using a specially designed Nuclear Magnetic Resonance (NMR) setup, the 1H, 23Na and 35Cl content in cementitious materials can be measured quasi-simultaneously and hence give us direct information on the interaction of the ions and the microstructure development. We have studied the influence factor, i.e., the water-cement ratio, on the microstructure development and the binding of Cl- and Na+. It was found that during the initial hydration stage more Cl- is bound in comparison to Na+ . This is reversed during the acceleration period after which there is a preference for binding of Na+ in comparison to Cl-. Increase of W/C ratio results in less binding capability of Na+ and Cl-.

Characteristics of fly ash(FA) blended mortars (50%, 70% and 90%) at different curing ages (28 days and 180 days) under ammonium chloride solution(ACS) leaching were investigated. Mass loss under leaching, initial CaO content, Ca(OH)2 content(CH), content of chemical bonded water, and hydration degree of blended pastes were tested by XRF and DSC-TG. Based on correlations between initial CaO content and CH content in blended pastes, correlations between mass loss under leaching and initial CaO content were analyzed, as well as effects of hydration degree of blended pastes and chemical bonded water in blended pastes. Results showed that FA blended mortars experienced a mass-loss period along with immersion in ACS, either 28-day curing regime or 180-day curing regime, and FA could minimize this mass loss obviously. Effects of hydration degree of FA blended pastes on this mass loss were feeble, but remarkable fluctuations could be made by chemical bonded water of FA blended pastes. Effect of FA against ACS leaching should be owed to its pozzolanic reaction which might neutralize attacks from ACS. However, this effect of FA against ACS leaching would weaken as long as alkaline environment increasingly extinguished. Therefore, excessive dosages of FA should be careful for structures and buildings experiencing solution leaching attacks. According to correlations with mass loss under solution leaching attacks, characteristic of initial CaO content in FA blended pastes could be regarded as one effective evaluation against solution leaching attacks.

Bleeding can be described as water coming out from fresh cement paste, which not only affects the homogeneity at fresh stage but also decides the hardened state structure. Previous studies have focused on the determination or simulation of the bleeding extent of fresh cement paste and give objective conclusions. However, there are rare researches about the influence of bleeding on the final structure of cement paste. In this study we have monitored the cement paste with various bleeding caused by water cement ratio and slag replacement. The microstructure development of cement paste from top to bottom was measured by using lowfield NMR with Hahn spin sequence from 6 h to 72 h. Results showed that within 4.4 mm bleeding thickness the bleeding will decrease the slope of the void ratio as a function of distance which suggests a homogeneous structure is formed. However, when the bleeding water thickness is higher than 4.4 mm, hydration would lead to a heterogeneous structure. Detailed discussions on the connection between the bleeding and the final structure are also presented in this paper.

Characteristics of fly ash(FA) blended mortars (50%, 70% and 90%) at different curing ages (28 days and 180 days) under ammonium chloride solution(ACS) leaching were investigated. Mass loss under leaching, initial CaO content, Ca(OH)2 content(CH), content of chemical bonded water, and hydration degree of blended pastes were tested by XRF and DSC-TG. Based on correlations between initial CaO content and CH content in blended pastes, correlations between mass loss under leaching and initial CaO content were analyzed, as well as effects of hydration degree of blended pastes and chemical bonded water in blended pastes. Results showed that FA blended mortars experienced a mass-loss period along with immersion in ACS, either 28-day curing regime or 180-day curing regime, and FA could minimize this mass loss obviously. Effects of hydration degree of FA blended pastes on this mass loss were feeble, but remarkable fluctuations could be made by chemical bonded water of FA blended pastes. Effect of FA against ACS leaching should be owed to its pozzolanic reaction which might neutralize attacks from ACS. However, this effect of FA against ACS leaching would weaken as long as alkaline environment increasingly extinguished. Therefore, excessive dosages of FA should be careful for structures and buildings experiencing solution leaching attacks. According to correlations with mass loss under solution leaching attacks, characteristic of initial CaO content in FA blended pastes could be regarded as one effective evaluation against solution leaching attacks.

As an internal curing material, superabsorbent polymers (SAPs) can effectively reduce the risk of volume shrinkage of cement-based materials. By preparing the cement paste mixed with SAPs, the amount of pre-absorbed water and the water-cement ratio of paste on the water absorption-release behavior in the fresh cement paste were studied by using 1H low-field NMR. The results showed that when the water-cement ratio was 0.30, the SAPs without pre-absorption could absorb the mixing water from the fresh paste and stored the mixing water in the SAPs relatively stable, while the pre-absorbed SAPs released the absorbed water into the paste rapidly, and the more pre-absorbed water, the faster the water released after mixing. When the watercement ratio was increased to 0.40, the mixing water absorbed by SAPs without pre-absorption was more than that absorbed by SAPs when the water-cement ratio was 0.30, but in the system with super high water-cement ratio of 0.50, the SAPs cannot absorb mixing water from the paste after mixing.

With freshwater getting scares seawater, i.e., water containing NaCl, can become the only viable option for making concrete. Although a lot of research had been directed to understanding the role of water in cement hydration, not much is known about the interaction of the Na+ and Cl- with cement paste during drying. A problem is that available techniques like, i.e., XRD, SEM, and EDX, for measuring the microstructure and the methods for determining the concentration of Na+, Cl- ions in pore solutions are either indirect or invasive and moreover often destructive, which consequently may lead to inadequate interpretations. Using a specially designed Nuclear Magnetic Resonance (NMR) setup, the 1H, 23Na and 35Cl content in cementitious materials can be measured quasi-simultaneously and hence give us direct information on the interaction of the ions and the microstructure development. We have studied the influence factor, i.e., the water-cement ratio, on the microstructure development and the binding of Cl- and Na+. It was found that during the initial hydration stage more Cl- is bound in comparison to Na+ . This is reversed during the acceleration period after which there is a preference for binding of Na+ in comparison to Cl-. Increase of W/C ratio results in less binding capability of Na+ and Cl-.