Maturity and Strength Development of Mortar with Antifreezing Admixture at Temperatures Lower than 0℃

This study investigated the e_ect of temperature and time at temperatures lower than 0℃ on mortar mixed with antifreezing admixture to determine the temperature–time function with the aim of expressing the e_ect universally. As a result, the maturity equation for temperatures lower than 0℃ proposed in previous studies was verified to be applicable to type-B blast furnace slag cement. The applicability of this equation at temperatures lower than 0℃ had not been investigated hitherto. The strength development attributable to the e_ect of the antifreezing admixture can be expressed as the reference temperature, and the reduction in the chemical potential of water chemical potential reduction was found to depend on the reaction rate. A new maturity equation for temperatures lower than 0℃ was proposed considering the e_ect of the antifreezing admixture

Performance Evaluation of Precast Concrete Using Microwave Heating Form

The purpose of this study is to evaluate the temperature distribution, strength development, porosity, scanning electron microscopy observation, shrinkage, and surface properties of concrete in order to apply microwave heat curing to the precast method and to analyze the CO2 emissions and economic feasibility of microwave heat curing. The heating of a steel form by microwave heating enabled concrete to be efficiently cured at a temperature within a range of _5 _C. After the curing, demolding strength could be cleared through the densification of the concrete by decreasing the porosity of the concrete. Microwave heat curing exhibited excellent performance compared to conventional steam curing in terms of efficient temperature control, occurrence of cracks due to shrinkage, surface condition of concrete after curing, economic efficiency, and CO2 emissions. However, verification and supplementation based on actual data are necessary so that environments applicable to the various sizes and shapes of forms can be prepared

Investigation of the Relationship between Compressive Strength and Hydrate Formation Behavior of Low-Temperature Cured Cement upon Addition of a Nitrite-Based Accelerator

When concrete is used for construction in cold-temperature regions, cold-resistant accelerators based on calcium nitrite (Ca(NO2)2) and calcium nitrate (Ca(NO3)2) are added to prevent early freezing damage. Although cold-resistant accelerators increase the early compressive strength and prevent early freezing damage by promoting cement hydration, the strength enhancement e_ect owing to the formation of such hydrates has not been evaluated quantitatively thus far. This study covers various types of analysis to understand the relationship between cement hydrate formation behavior and strength development upon the addition of varying amounts of nitrite-based accelerator. We find that the early compressive strength is enhanced by the addition of nitrite-based accelerator via the promotion of the relative production of monosulfate and C-S-H in the early age. However, the development of compressive strength decreases with an increase in the curing age. Furthermore, we find that the promotion of hydration reactions at an early age with the addition of nitrite-based accelerator can a_ect the formation ratio of each hydrate at a late age. We believe our findings can significantly contribute to developments in concrete application and allied fields

Modeling of Concrete Mixed with Expansive Additives

In this study, the Mechanical properties, volume changes and creep of concrete mixed with expansive additives, which is used as a countermeasure for cracking and shrinkage, were modeled and the model was verified. In addition, the generated stress was estimated using the modeled creep phenomenon to calculate changes in the stress under the restraint condition, thus allowing a comparison with experiment to verify the model’s applicability and the validation of the stress prediction technique.特

Influence of aggregate materials characteristics on the drying shrinkage properties of mortar and concrete

This paper presents an experimental study to clarify the effect of various aggregate materials characteristics on the drying shrinkage property in mortar and concrete specimens incorporating fourteen kinds of fine aggregate materials (standard sand, natural sand, marine sand, various kinds of slag-type sand, and various kinds of crushed sand) and three kinds of coarse aggregate materials (andesite gravel, hard sandstone gravel, and limestone gravel). The test results revealed that the characteristics of fine and coarse aggregate materials play an important role in controlling the drying shrinkage property of mortar and concrete, respectively. Limestone sand and blast furnace slag sand can restrain the drying shrinkage of mortar specimens about 22% and 30%, respectively, compared to the case of mortar incorporating standard sand. The drying shrinkage strain of concrete specimens proportionally increases with the increase of aggregate shrinkage strain, specific surface area and 6–30 nm in diameter pore volume of aggregates, which implies the significant influence of aggregate characteristics on drying shrinkage development in concrete. It was also found that the drying shrinkage property in concrete can be affected by the static modulus of elasticity and total amount of water content, in which the water absorption ratio, unit mass of aggregate and unit water content were considered. Finally, the experimental results presented are useful information for providing a good perspective for the concrete mixture design practices taking into consideration that concrete drying shrinkage could be controlled by appropriate aggregate characteristics and reducing the total amount of water content

The Required Compressive Strength and Prehardening Time to Prevent Damage to High Flowing Concrete from Frost Damage at Early Ages

This investigation was undertaken to develop data on the early frost resistance of high flowing concrete made either with various type of mineral fine powders or viscosity agents. From the results of this investigation it was found that the test cylinders cast from air entrained concrete (ie., air>3.5%)which cured up to 23°D.D prior to freezing, performed with satisfactory resistance to early freezing and thawing cycles. However the 28 days strength ratio of all AE specimens were above 100%. This study recommends early continuous protection until AE high flowing concrete has attained compressive strength of 70 to 80 kg/cm^2

Distribution Map of Frost Resistance for Cement-Based Materials Based on Pore Structure Change

This paper presents a prediction method and mathematical model based on experimental results for the change in pore structure of cement-based materials due to environmental conditions. It focuses on frost damage risk to cement-based materials such as mortar. Mortar specimens are prepared using water, ordinary Portland cement, and sand and the pore structure is evaluated using mercury intrusion porosimetry. New formulas are proposed to describe the relationship between the pore structure change and the modified maturity and to predict the durability factor. A quantitative prediction model is established from a modified maturity function considering the influences of environmental factors like temperature and relative humidity. With this model, the frost resistance of cement-based materials can be predicted based on weather data. Using the prediction model and climate data, a new distribution map of frost damage risk is created. It is found that summer weather significantly affects frost resistance, owing to the change in pore structure of cement-based mortar. The model provides a valuable tool for predicting frost damage risk based on weather data and is significant for further research

Influence of Restrained Condition on Mechanical Properties, Frost Resistance, and Carbonation Resistance of Expansive Concrete

This paper presents the results of an experimental investigation of the effect of the restrained condition on the mechanical properties, frost resistance, and carbonation resistance of expansive concrete with different water-binder ratios. In this study, length change ratio test, expansion strain test, compressive strength test, mercury intrusion porosimetry test, underwater weighing test, freezing-thawing test, and accelerated carbonation test were performed to evaluate the mechanical properties, pore size distribution, total porosity, and durability of expansive concrete under both restrained and unrestrained conditions. The test results indicate that the length change ratio and expansion strain of the expansive concrete were controlled by the restrained condition. The compressive strength of expansive concrete was enhanced by the triaxial restraining when the amount of expansive additive was 40 kg/m(3) of concrete. Two hypotheses were described to explain the change of pore structure change expansive mortar. The results also indicate that the carbonation resistance and frost resistance were improved by the uniaxial restrained condition. Furthermore, the effect of the restrained condition must be considered to evaluate not only the experimental results of the expansive concrete with a high EX replacement level but also the expansive concrete combining other cement replacement materials

Potent amyloidogenicity and pathogenicity of Aβ43.

The amyloid-β peptide Aβ42 is known to be a primary amyloidogenic and pathogenic agent in Alzheimer\u27s disease. However, the role of Aβ43, which is found just as frequently in the brains of affected individuals, remains unresolved. We generated knock-in mice containing a pathogenic presenilin-1 R278I mutation that causes overproduction of Aβ43. Homozygosity was embryonic lethal, indicating that the mutation involves a loss of function. Crossing amyloid precursor protein transgenic mice with heterozygous mutant mice resulted in elevated Aβ43, impairment of short-term memory and acceleration of amyloid-β pathology, which accompanied pronounced accumulation of Aβ43 in plaque cores similar in biochemical composition to those observed in the brains of affected individuals. Consistently, Aβ43 showed a higher propensity to aggregate and was more neurotoxic than Aβ42. Other pathogenic presenilin mutations also caused overproduction of Aβ43 in a manner correlating with Aβ42 and with the age of disease onset. These findings indicate that Aβ43, an overlooked species, is potently amyloidogenic, neurotoxic and abundant in vivo