Query: low shrinkage cement

title: Anti cracking low shrinkage deformation fiber cement product and production method thereof
abstract: The invention relates to an anti cracking low shrinkage deformation fiber cement product and a production method thereof. Concretely, a novel fiber reinforced cement product with an excellent anti cracking function and low shrinkage deformation is realized through an ultra short fiber, low elasticity modulus short fiber and high elasticity modulus long fiber composite reinforced cement base material by simultaneously adopting high efficiency additives (a high efficiency water reducing agent, a thickening agent, an expanding agent and the like) The product comprises a flexible anti cracking surface layer and a fiber reinforced cement structural layer, has a simple and resaonable structure, is convenient and easy in production construction and can be applied to projects, such as building external wall decorative enclosure, indoor engineering construction as well as roads, bridges and the like with higher requirements on the strength and the durability of the cement base material.

title: Carrageenan based superabsorbent biopolymers mitigate autogenous shrinkage in ordinary portland cement
abstract: We report the synthesis and characterization of biobased superabsorbent copolymers from k carrageenan and poly(acrylic acid) that mitigate autogenous shrinkage in ordinary portland cement paste. Synthesized via free radical graft polymerization, the biobased superabsorbent polymers (SAPs) were characterized with regard to their thermochemical properties and swelling behavior in both aqueous and ionic solutions. The biobased SAPs were incorporated into cement paste to investigate their ability to mitigate autogenous shrinkage cracking in high performance concrete. Results demonstrate that the biobased SAPs absorb up to 438 and 94 [g/g] (by mass) in aqueous and ionic solutions, respectively, after 24 h. Furthermore, the biobased SAPs were successful in mitigating shrinkage in low water to cement ratio pastes. While the control paste exhibited negative strain and ultimate shrinkage cracking, the samples containing biobased SAP experienced net positive expansion during cement hydration.

title: Internal Relative Humidity, Autogenous Shrinkage, and Strength of Cement Mortar Modified with Superabsorbent Polymers
abstract: Laboratory evaluations were performed to investigate the effect of internal curing (IC) by superabsorbent polymers (SAP) on the internal relative humidity (IRH) autogenous shrinkage, coefficient of thermal expansion (CTE) and strength characteristics of low water cement ratio (w/c) mortars. Four types of SAP with different cross linking densities and particle sizes were used. Test results showed that the SAP inclusion effectively mitigated the IRH drops due to self desiccation and corresponding autogenous shrinkage, and the IC effectiveness tended to increase with an increased SAP dosage. The greater the cross linking density and particle size of SAP, the less the IRH drop and autogenous shrinkage. The trend of autogenous shrinkage developments was in good agreement with that of IRH changes, with nearly linear relationships between them. Both immediate deformation (ID) based and full response based CTEs were rarely affected by SAP inclusions. There were no substantial losses in compressive and flexural strengths of SAP modified mortar compared to reference plain mortar. The findings revealed that SAPs can be effectively used to reduce the shrinkage cracking potential of low w/c cement based materials at early ages, without compromising mechanical and thermal characteristics.

title: Autogenous shrinkage of low water binder ratio cement pastes with supplementary cementitious materials
abstract: High performance cementitious materials are sensitive to early age cracking, mainly due to the large magnitude of autogenous shrinkage, which is closely related to the internal relative humidity (RH) decrease and capillary pressure induced by self desiccation in the cement matrix. However, there is debate about the determination of time zero, the time at which autogenous shrinkage begins to develop, which causes great difficulty in comparing the results provided in the exiting researches. This study presents an accurate determination of time zero based on the relationship between the internal RH and autogenous shrinkage of cementitious materials. According to the time zero, the effect of replacements of cement by supplementary cementitious materials on the autogenous shrinkage was investigated for the early age cement pastes with low water/binder ratio. The autogenous shrinkage was conducted according to the standard method ASTM C1698. Internal RH was performed on the sealed cement pastes at very early age by conventional method of hygrometer. Setting time was determined by the Vicat needle apparatus according to the standard method ASTM C191. The results could potentially explain the mechanism of autogenous shrinkage at early age in mixtures with supplementary cementitious materials.

title: Use of rice husk ash for mitigating the autogenous shrinkage of cement pastes at low water cement ratio
abstract: It is well recognized that the high risk of early age micro crack of HPC/UHPC is attributed to the large magnitude of early age autogenous shrinkage caused by self desiccation in binder hydration. Over the years, several methods have been proposed to mitigate autogenous shrinkage based on internal curing theory, and a better internal curing agent is always being sought. Rice husk ash (RHA) was recognized having potencial to be an internal curing agent. In this paper, the effect of RHA on mitigating the autogenous shrinkage has been evaluated by different mean particle sizes of RHA, and the internal RH change was measured at the same situation. The results show a high efficiency of RHA for internal curing purpose, to drastically reduce the autogenous shrinkage of cement pastes. Comparing to the cement paste without RHA, the internal RH results show that the internal RH in pastes with RHA is evidently higher at either early or later ages. These were addressed in order to explain the mechanism RHA mitigates the autogenous shrinkage of pastes.

title: Effect of water to cement ratio and curing method on the strength, shrinkage and slump of the biosand filter concrete body.
abstract: The biosand filter is a household level water treatment technology used globally in low resource settings. As of December 2016, over 900,000 biosand filters had been implemented in 60 countries around the world. Local, decentralized production is one of the main advantages of this technology, but it also creates challenges, especially in regards to quality control. Using the current recommended proportions for the biosand filter concrete mix, slump was measured at water to cement ratios of 0.51, 0.64 and 0.76, with two replicates for each level. Twenty eight day strength was tested on four replicate cylinders, each at water to cement ratios of 0.51, 0.59, 0.67 and 0.76. Wet curing and dry curing were compared for 28 day strength and for their effect on shrinkage. Maximum strength occurred at water to cement ratios of 0.51 0.59, equivalent to 8 9.3 L water for a full scale filter assuming saturated media, corresponding to a slump class of S1 (10 40 mm) Wet curing significantly improved strength of the concrete mix and reduced shrinkage. Quality control measures such as the slump test can significantly improve the quality within decentralized production of biosand filters, despite localized differences in production conditions.

title: Role of alcohol ethylene oxide polymers on the reduction of shrinkage of cement paste
abstract: Concrete drying shrinkage is a major practical problem, but it can be ameliorated by means of "shrinkage reducing agents" (SRAs) Water vapor sorption isotherms and low temperature DSC measurements suggest that alcohol ethylene oxide polymers (AEOPs) with a better hydrophilic lipophilic (HL balance are present in meso pores in which water molecules evaporate from 75% RH to 40% RH. Short term drying shrinkage measurements show that the better HL balanced AEOPs reduce irreversible shrinkage, which occurs mainly from 75% RH to 40% RH during the first drying. Based on the similarity between corresponding RH regions, it is concluded that the better HL balanced AEOP in relevant meso pores hinders agglomeration of C S H during the first desorption to mitigate the irreversible shrinkage and reduce the first drying shrinkage.

title: Effect of napier grass ash on the autogenous shrinkage of low water binder ratio cement based materials
abstract: This work presents an experimental investigation on the effect of Napier grass ash (NGA) on the early age autogenous shrinkage of NGA blended cement paste with low water/binder ratio. Further burnt process was conducted on the as received raw NGA to decrease the carbon content, and comparison study was performed. Comprehensive tests were performed on the sealed samples to evaluate the behavior of autogenous shrinkage and self desiccation in NGA blended cement pastes with low water/binder ratio 0.25. The autogenous shrinkage was conducted according to the standard method ASTM C1698. Setting time was determined by the Vicat needle apparatus according to the standard method ASTM C191. Internal RH measurement was performed to reveal the self desiccation process of the sealed cement pastes at very early age. Considering the relationship between the self desiccation and autogenous shrinkage of cementitious materials, a new 'time zero' was proposed. The effect of replacement of cement by NGA on the autogenous shrinkage of low water/binder ratio cement pastes was revealed by comparison study between the autogenous shrinkage measured from final setting time as defined in standard method ASTM C1698 and the new 'time zero'

title: Autogenous shrinkage of zeolite cement pastes with low water binder ratio
abstract: Self desiccation is one common phenomenon of high performance cementitious materials characterized by low water to cementitious material ratio (w/c) Autogenous shrinkage is closely related to the internal relative humidity (RH) drop and capillary pressure induced by self desiccation in the cement pastes. However, there is debate about the determination of time zero, the time at which autogenous shrinkage begins to develop. The objective of this study is to provide an accurate determination of time zero based on the relationship between the internal RH and autogenous shrinkage of low w/c ratio cement pastes. And according to the time zero, cement pastes blended with zeolite were prepared to investigate the potential of zeolite as internal curing agent. The autogenous shrinkage was conducted according to the standard method ASTM C1698. Internal RH was performed on the sealed cement pastes at very early age by conventional method of hygrometer. Setting time was determined by the Vicat needle apparatus according to the standard method ASTM C191. Experimental results revealed that no internal RH drop was observed around the final setting time determined by the Vicat method. Besides, a knee point was observed in the shrinkage curve at the time when the internal RH began to decrease. This is the so called time zero. And zeolite was found to be a potential internal curing agent according to the autogenous shrinkage tests measured from the new time zero.

title: Tensile response of low clinker UHPFRC subjected to fully restrained shrinkage
abstract: This paper addresses the tensile response of Strain Hardening Ultra High Performance Fiber Reinforced Concretes (SH UHPFRC) subjected to restrained autogenous shrinkage deformations under full and partial restraint conditions, right after casting and until one month. The development of autogenous shrinkage and corresponding eigenstresses under various degrees of restraint were studied for two types of mixes; Mix I with type I cement and silica fume, and Mix II with silica fume and 50% mass replacement of type I cement with limestone filler. The tests under 100% restraint conditions are the first of their kind on SH UHPFRC and the results show that under these conditions, the material enters into the strain hardening domain of the tensile response. The development of eigenstresses was much slower in the Mix II when compared to that of Mix I. The development of the dynamic elastic modulus and heat of hydration were also studied and put into perspective.