Correlation of porosity and properties of recycled fine aggregate concrete with fly ash

In this paper, we presented the experimental discussion of samples of recycled aggregate concrete with replacement of natural fine aggregate by recycled fine aggregate. Three mix kinds were produced and, for each of these three kinds, two levels of water to blinder ratio were used with 0%, 10% and 20% of FA. The result of the tests of drying shrinkage and compressive strength of recycled concrete were used for comparison with tests of mercury intrusion porosimetry (MIP), in which the cumulative pore volume and different intervals of pore volume were studied at ages of 28 and 91 days. Correlation graph of compressive strength and cumulative pore volume might be predicted with given W/B, days and FA of the concrete or none given and drying shrinkage might be predicted with given FA

A study on properties of concrete with dry fly ash and fly ash slurry stored with stirring

In the evaluation of concrete sustainability, what constitutes "sustainable" to one region may vary from another. This often leads to methodological forms of uncertainties that makes the evaluation process more complex. As such, this paper aims to quantify the effect of uncertainties in the regional context on the sustainability evaluation of concrete materials. This is carried out by quantifying the regional context through establishing a weighting scheme and then integrating the obtained weights into the sustainability analysis of concrete materials in tandem with uncertainty analysis. Japan is used as a case study because although it relatively appears as a homogeneous country, its prefectures possess unique characteristics that may make the sustainability evaluation of concrete materials vary across prefectures. Cluster analysis is carried out in the 47 prefectures of Japan using a set of regional context indicators. Five clusters are identified with varying characteristics and these are translated into different weighting schemes. The established weights are used in the sustainability evaluation of concrete materials using multi-criteria decision-making analysis. The results showed that one mix is the most sustainable for four of the clusters and a different mix is the most sustainable for the remaining cluster. When uncertainty analysis is conducted, the effect of the weights in the sustainability evaluation is explained by examining the average scores of the concrete mixes and the variance of the scores across the five clusters. This investigation facilitated the understanding of how regional differences and the uncertainties associated with it impact the evaluation of concrete sustainability

Development of Flotation Device for Removing Unburnt Carbon in Fly Ash for Use in Hardened Cementitious Materials

The unburned carbon in fly ash inhibits the performance of concrete. A device using the flotation method to remove unburned carbon in fly ash was developed, and the operating condition of the device was experimentally examined. According to the results, the device was able to remove unburnt carbon from fly ash by using the installed micro bubble nozzles and a whirl-type pump. The removal efficiency of unburnt carbon improved when prior forced stirring was carried out by a concrete mixer for 3 min, and a scavenger was added into the fly ash slurry at a density of about 60 wt%. It has also been confirmed that the method of circulating water is more effective than the method of not circulating water. The elements of the modified fly ash slurry (MFAS) have also been experimentally confirmed as not being too different from untreated fly ash, except for the fact that the content of unburned carbon is reduced. The compressive strength and drying shrinkage characteristics of concrete made with MFAS were investigated. The use of MFAS will reduce the performance of concrete compared to that of ordinary concrete. This shows that in a certain range (15–30%), the influence of MFAS on drying shrinkage is constant. The static elastic modulus and dynamic elastic modulus were also investigated. The above results show that the application of MFAS prepared by the flotation method to concrete is feasible

The Effects of Curing Temperature on CH-Based Fly Ash Composites

Curing temperature affects the compressive strength of cement paste systems via the pozzolanic reaction. However, different processes, climates, and weather conditions often result in different initial curing temperatures. The relationship between curing temperature and compressive strength is still an underexplored domain. To explore the effect of curing temperature on calcium hydroxide (CH)-based fly ash composites, fly ashes from different carbon sources were used to make CH-based composites, and the compressive strength, reaction rate, CH content, and C-S-H generation were analyzed. The correlation between the reaction rate and C-S-H content was analyzed. High-temperature curing improved the compressive strength of the cement paste system by affecting the CH-based reaction rate in the initial stage, with the highest initial reaction rate reaching 28.29%. However, after cooling to constant temperature, high-temperature curing leads to a decrease in CH and C-S-H content. The average decrease rate of calcium hydroxide content under high temperature curing is 38%, which is about 2.38 times that of room-temperature curing conditions. This led to a decrease in the compressive strength of the cement paste. Therefore, the performance of CH-based fly ash composites produced by low-temperature curing was superior to that of composites produced by high-temperature curing

Study on the Effect of Recycled Fine Aggregate Qualities on Fly Ash/GGBS-Based Geopolymer Mortar

The rapid expansion of construction, fueled by industry and economic and population growth, has exacerbated the challenge of managing construction waste, especially concrete waste. One promising solution lies in the utilization of recycled fine aggregate (RFA), especially in combination with the emerging geopolymer technology, an innovative alternative to traditional cement. This study systematically explores the effects of incorporating varying qualities and quantities of RFA into geopolymer mortars. By using GGBS and FA as raw materials and replacing natural aggregates (NA) with RFA at different rates (25%, 50%, 75%, and 100%), the research investigates the fresh properties, mechanical characteristics, and drying shrinkage of geopolymer mortar. Key findings reveal that RFA significantly influences the flowability of geopolymer mortar: when RFA content is above 75%, preprocessed RFA (with particles below 0.15 mm removed) has substantially improved flowability, increasing it more than 20%. The critical impact of RFA preprocessing on enhancing mechanical properties and the higher the inclusion level (above 75%), the more pronounced is the advantage in enhancing the compressive strength compared to unprocessed RFA. Additionally, RFA was found to contribute to a denser interfacial transition zone (ITZ) than natural aggregate, which helps maintain the compressive strength at increased RFA dosages. Contrary to findings in cement mortar, a positive correlation exists between pore volume and compressive strength in geopolymer mortar incorporating RFA. This study underscores the potential of refined RFA preprocessing methods in advancing sustainable construction, highlighting avenues for the broader application of RFA in geopolymer mortar

The Effect of Cementitious Materials on the Engineering Properties and Pore Structure of Concrete with Recycled Fine Aggregate

With the rapid development of urbanization, the construction industry consumes a lot of cement and produces a large amount of construction waste. To overcome this situation, the rational use of recycled aggregate produced from waste concrete is one of solutions. In some countries, the building industry has approved the use of recycled coarse aggregates in concrete, with some limits. However, practically all existing standards and regulations prohibit the use of recycled fine aggregate (RFA) in concrete. Therefore, study on improving the performance of RFA concrete is vital. In this study, the effects of fly ash and GGBS on concrete with RFA were investigated. Compressive strength, pore structure, drying shrinkage and accelerated carbonation were tested. The correlation between the pore structure and properties of concrete was analyzed. The results show that adding fly ash and GGBS to RFA concrete increased its compressive strength, modified pore structure, reduced drying shrinkage, and even achieved higher compressive strength and lower drying shrinkage than normal concrete. The compressive strength was mainly affected by the capillary pores, and the carbonation was mainly affected by the gel pores

Estimation on Applied Period of Hot Weather Concreting under Global Warming

On hot weather concreting, for the proper execution planning to prevent many problems on concrete quality, it is Important to estimate the length and severity of hot weather ambience. In this study，the methods were discussed using the data opened to the public by Japan Meteorological Agency. The method described in JASS5 tends to estimate the period shorter due to the effect of recent global warming. The presented method using the mean value of ambient temperature at the nearest ten years could estimate better than the traditional one using the normal values. Additionally, it was shown that the length and severity of hot weather ambience were correlated well

Minimum Curing Period on Hot Weather Concreting : Effect of Deteriorated Layer on Compressive Strength

This research examined the minimum curing period of concrete in hot weather concreting. As a result of the experiment using the full scale concrete wall specimens(experiment I), it was clarified that the surface part of the concrete walls removed frameworks in the early age less than 3 days deteriorated apparently, although the significant difference in measured values of concrete strength did not be observed according to the difference of its curing period. The reason that the effect of the curing period on compressive strength were not obvious as compared with that on the porosity of cement hydrates and the carbonation were explained on the relation between the strength and the thickness of the deteriorated layer(experiment II)

Evaluation of Carbonation for Concrete Containing Large Quantity of Fly Ash

In this study, we examined carbonation of fly ash concrete which promoted pozzolanic reaction by increasing curing temperature before an accelerated carbonation test, and compared our results to long-term carbonation test results. As a result, it was found that the carbonation rate of concrete exposed under natural conditions for 10 years was closer to that of specimens cured in water or an incubator at 40℃ than to that of specimens cured in water at 20℃ which is the curing temperature specified in JIS A 1153. Consequently, the accelerated carbonation test method by the high temperature curing will be valuable for evaluating the carbonation of fly ash concrete exposed under natural conditions