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Ong, K. Microwave-assisted concrete technology : production, demolition, and recycling. Request this item to view in the Library's reading rooms using your library card. To learn more about how to request items watch this short online video. You can view this on the NLA website. Login Register. Advanced search Search history.

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Cite this Email this Add to favourites Print this page. You must be logged in to Tag Records. Gary Ong, Ali Akbarnezhad. In the Library Request this item to view in the Library's reading rooms using your library card. The absorption ratio also decreased with an increased coarse aggregate ratio, but not as substantially as the absorption ratio. On the other hand, the water ratio showed a point of inflection at 1.

Assumed absorption ratio of recycled fine aggregate by variance analysis: a water ratio; b coarse aggregate ratio; and c abrasion crusher time. Table 8 shows the results of the F-test performed on each experimental parameter after performing ANOVA on the solid volume percentage results.

## Assessing a Reclaimed Concrete Up-Cycling Scheme through Life-Cycle Analysis

The F values of A water ratio , B coarse aggregate ratio , and C abrasion time were found to be 0. The sum of squares of A water ratio was smaller than the error term and, thus, A water ratio was included in the error for pooling. Table 9 shows the pooling results. C abrasion time was higher than Thus, C abrasion time was found as the most significant parameter even for the solid volume percentage, whereas A water ratio and B coarse aggregate ratio were found to be insignificant.

Figure 5 shows the changes in the values estimated for the population mean for each level of the experimental parameters with respect to the solid volume percentage. Similar to the experimental results for density and absorption ratio, an increase in the abrasion time substantially increased the solid volume percentage.

The increase was especially dramatic between 5 and 10 min of abrasion time. On the other hand, an increase in the water ratio or the coarse aggregate ratio caused only a slight increase in the solid volume percentage. An increase of processing time in abrasion crusher results in an increase of friction between the recycled fine aggregates. Therefore, it leads to accelerating the removal of cement paste from the recycled fine aggregates, enhancing the grain size of aggregates, etc. Finally, these actions improve the solid contents in aggregates, which is shown in Figure 5 c. Assumed solid volume of recycled fine aggregate by variance analysis: a water ratio; b coarse aggregate ratio; and c abrasion crusher time.

RSM was applied with the aim to determine the abrasion conditions that would induce optimum performance based on the results derived by applying an orthogonal array design. The target performance levels were over oven-dry density and less than 3. It should be noted that the recycled fine aggregate, which meets the quality standard, has been limited to use in concrete manufacture. To overcome it, the quality standard for the natural fine aggregate, which is over density and less than 3.

Moreover, as analyzed above, A water ratio was excluded as it was determined to have low significance, and RSM was applied only for B coarse aggregate ratio and C abrasion time. The results were then compiled to derive the optimum abrasion conditions. Relationship between two factors, i. Table 10 shows the results of applying RSM with respect to density in cases where there were changes in B coarse aggregate ratio and C abrasion time. R2, the coefficient of determination for the regression equation, with respect to density, was 0.

Figure 6 shows the results of applying RSM in relation to the oven-dry density of recycled fine aggregates that were obtained from B coarse aggregate ratio and C abrasion time. Line T in Figure 6 is a line that satisfies the target performance level for the oven-dry density, which was 2.

In the case of recycled fine aggregates, increased density results in quality improvement and, thus, the upper part of Line T satisfies the target performance level. The target performance level was satisfied at an abrasion time of over 11 min for a coarse aggregate ratio of 1. Increased abrasion time means increased input energy, and this improves the quality of recycled aggregates. Increasing the coarse aggregate ratio, on the other hand, results in a relative decrease in the target amount of recycled fine aggregates as the capacity of the abrasion device is fixed.

Therefore, these variables should be considered to determine the optimum coarse aggregate ratio and abrasion time. Analysis response surface for the density of recycled fine aggregate drive from coarse aggregate ratio and abrasion time. Again, the relationship between two factors, i. Table 11 shows the results of applying RSM with respect to the absorption ratio in cases where there were changes in B coarse aggregate ratio and C abrasion time. R2, the coefficient of determination for the regression equation with respect to absorption ratio, was 0.

Figure 7 shows the results of the contour analysis of the optimum abrasion range for the absorption ratio according to B coarse aggregate ratio and C abrasion time. The results show that, similar to density, an abrasion time of over 15 min and fine aggregate and coarse aggregate ratio of over 1 resulted in a performance level exceeding the target level proposed in the quality standards for recycled fine aggregates, which is up to the standard in comparison to natural fine aggregates. Analysis response surface for the absorption ratio of recycled fine aggregate derived from the coarse aggregate ratio and abrasion time.

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## Advanced Concrete Technology (Book with DVD)

An optimization technique is applied to seek the optimum abrasion conditions. Typically, an optimization problem with constraints can be expressed as:. It is difficult to determine the global maximum or minimum solution if the objective function does not have one or more constraints. Therefore, a penalized objective function is adopted and is expressed as follows [ 28 ]:. In this study, the productivity per day, i. It should be noted that the actual equation for the unit productivity is very complicated and must consider various factors, such as human labor, material cost, delivery fee, machine operations time, etc.

Rather, it is simply assumed like a unit time to product, which is 8 h per day divided by the abrasion time, multiplying the amount of coarse aggregates, and is expressed as:. Design variables, i. Density and absorption time are derived and are expressed by means of design variables in Table 10 and Table 11 , respectively. Assumptions for density and absorption time are introduced for the optimization problem in this study, i. In other words, density should be greater than the target performance level, i.

Absorption time should be less than the target performance level, i. Thus, constraints are expressed as:. Optimization has been performed using MATLAB [ 30 ] and Figure 8 shows the optimum mixing conditions satisfying the required performance level that was determined based on Figure 6 and Figure 7 , showing the results of analyzing the density and the absorption ratio.

Thus, considering the productivity of the manufacture of recycled fine aggregates, it is deemed that it would be economical to feed relatively large amounts of coarse aggregates to reduce the production time. In addition, the optimum abrasion conditions for improved productivity and cost effectiveness would be an abrasion time of 8. In that case, the unit productivity was maximized and has a value of Typically, the recycled aggregates have a limited usage due to its low quality comparing with natural aggregates.

In this study, experimental testing has been conducted considering three factors, i. To do this, experimental plans have been arranged in a three-level system using the orthogonal design method. Overall, 27 experimental plans have been arranged in nine experimental levels. The abrasion conditions for the production of recycled fine aggregates have been derived using the response surface methods and its optimum conditions to maximize the production have been found using the Nelder-Mead sequential simplex algorithm with various constraints.

During the procedure, the unit production amount has been selected as the objective function. The following conclusions were made based on the results of this study conducted on the manufacturing method for recycled fine aggregates that satisfy the quality standards. Of the abrasion conditions, such as water ratio, coarse aggregate ratio, and abrasion time, abrasion time was found to have the most significant impact on the density change, while the water ratio had no significant impact.

## MDS: | LibraryThing

The results of reviewing the changes in the quality of recycled fine aggregates caused by varying the water ratio, coarse aggregate ratio, and abrasion time showed that, similar to the density experiment, abrasion time was found to have the most significant impact on the changes in the absorption ratio, and the trend in the changes was similar to that of the changes observed in density. The results of the abrasion experiment performed to determine the optimum conditions for the manufacture of recycled fine aggregates that satisfy the quality standards showed that an abrasion time of 8.

Therefore, it is advantageous to use pulverized materials to ensure the quality of the production efficiency and aggregate when the optimal abrasion conditions for producing the high-quality of the recycled aggregates are applied. Additionally, it gives more benefits in productivity and economics to use the recycled aggregates from deconstruction and demolition of reinforced concrete structures and will be helpful to save the limited amount of the natural aggregates and environmental protection.

Finally, it can be expected that a further study related to apply the recycled aggregates, having the improved quality, to the mortar and concrete in order to evaluate its material properties and stability. National Center for Biotechnology Information , U. Published online Jul Author information Article notes Copyright and License information Disclaimer. Received Jun 13; Accepted Jul Abstract There has been increased deconstruction and demolition of reinforced concrete structures due to the aging of the structures and redevelopment of urban areas resulting in the generation of massive amounts of construction.

Keywords: recycled fine aggregates, response surface methodology, design of experiment, orthogonal arrays, abrasion-crusher time, acid treatment. Introduction There has been increased deconstruction and demolition of reinforced concrete structures due to the aging of the structures and redevelopment of urban areas, i. Open in a separate window. Figure 1. Experimental Design and Method 2.

Experiment Design In general, the orthogonal design method [ 16 ], proposed by Genichi Taguchi, is an experimental design method that can reduce a number of experiments by means of sacrificing the information on the parameters effecting on the test results. Table 1 Experimental plan using the design of experiment. Table 2 The level of experiment. Experimental Methods The recycled fine aggregates, having a size of 5 mm or less, used in this experiment were obtained from Green and Environments Co.

Table 3 The physical properties of recycled fine aggregate.

Figure 2. Experiment process of the manufacture of high-quality of recycled fine aggregate. Measurement Method The testing on the quality of the recycled aggregates was conducted according to the items listed in the quality standards for recycled aggregates limited to recycled fine aggregates used in concrete manufacture , and of the physical properties specified in the quality standards, the most important quality characteristics of recycled fine aggregates were reviewed and a statistical analysis was performed on the results.