Properties and Novel Applications of Recycled Aggregates

Coal fly ash (CFA) Type F according to the American ASTM C standard and coal bottom ash (CBA) were obtained from a Spanish power plant (Carboneras, Spain). The corrosion process of the steel bar starts when the chloride ions reached the reinforcing bar.

Table 1. Properties of used cements and ashes: Coal bottom ash and coal fly ash (%).

Results and Discussion

Moreover, the most important parameter affecting the initiation of corrosion is the amount of coal ash, regardless of the type of ash. The evolution of the corrosion rate of the steel reinforcement embedded in the mortar specimens was more stable than the corrosion potential.

Figure 2. Time (a) and non-steady state (apparent) diffusion coefficient (b) vs. coal ash content.

Conclusions

Effect of chloride salt type on the critical chloride content of reinforcement corrosion in concrete. Mag. Effect of CaCl2 and NaCl from different sources on chloride threshold value for corrosion of steel reinforcement in concrete.

Recycled Mineral Raw Materials from Quarry Waste Using Hydrocyclones

Introduction

Materials and Methods 1. Characterization Tests

The content of aluminum oxide can be reduced because it is associated with clay components, but this cannot be said in the case of titanium oxide. During the preparation process, special attention was paid to preventing the formation of air bubbles in the mass.

Table 2. Quartz sand specifications.

Results and Discussion 1. Material Characterization

Table 9 and Figure 4 show the results obtained in the compressive strength tests performed in each case. In the case of some specific applications, the recycled product could not meet the required purity standard due to the concentration of titanium oxides in the product below the liquid.

Table 5. Major components in the sample (%).

SEM Image Analysis in Permeable Recycled Concretes with Silica Fume. A Quantitative

Materials and Methods 1. Materials

A histogram was used to determine the range of application (a plot of pixel frequency versus the value on the gray scale), which included the pixels in the range of values ​​from the initial (equal to zero) to the decrease in the last of the histogram frequency curves. After these procedures and the image calibration, the sector was built in the scope of the ITZ (theoretical ITZ thickness located between the aggregate and paste throughout all areas).

Table 1. Properties of the aggregates.

Thickness of the ITZ (μm)

It can be seen that for most samples there is a direct relationship between the increase in percentage porosity and the increase in the theoretical thickness of the ITZ. Therefore, it can be argued that the use of RCA in PC fabrication will result in an increase in ITZ porosity.

Unitary accumulated anhydrous material (%/μm)

In addition, a comparison of NCA 100 C and NCA 100 SF shows that the former contains a much higher percentage of anhydrous material at all theoretical ITZ thicknesses than the latter.

Thickness of ITZ (μm)

Future Research

Effect of different replacement of natural aggregate by recycled aggregate on performance characteristics of pervious concrete. Properties of pervious concrete made with air cooled electric arc furnace slag as aggregate. Construction.

Lime Treatment of Coal Bottom Ash for Use in Road Pavements: Application to El Jadida Zone in Morocco

Materials and Methods 1. The Origin of the Materials

The second part describes the experimental program, including the results obtained for the treatment of BA using lime and sand. The purity of BA is then evaluated using two methods: the sand equivalent (SE) method and the methylene blue method according to the NF P and NF P94-068 standards [22].

Figure 2. (a) Mortar prism (4 × 4 × 16 cm) (b) Compacted test tubes of bottom ash (R = 7 cm, h = 15 cm).

Results

The granulometric study of BA (see Figure 4) shows that their particle size distribution (PSD) is very close to that of sand. In the proposed pavement structure, we used TBA as a foundation layer instead of UGF2 (untreated aggregate for foundation layer type 2).

Figure 3. Mineralogical composition of bottom ash (BA) using X-ray diffraction.

Slag Substitution as a Cementing Material in Concrete: Mechanical, Physical and

Environmental Properties

• Materials
• Tests’ Descriptions
• Results and Discussion
• Conclusions

The porosity test results are shown in Table 4 and shown in Figure 2. Regardless of the percentages of cement replacement, it was observed that the LFS1 slag mixtures had high porosity, as its porosity increased significantly. LFS represents a loss of flexural strength that is half of the loss of compressive strength.

The results of the leaching tests of concrete mixes with slag are similar to the results of traditional concrete.

Table 1 shows the major components of the slags studied; the rest of secondary compounds are described in another paper which used the same slags [22].

Estimation of Recycled Concrete Aggregate’s Water Permeability Coefficient as Earth Construction

Analytical Method

• Literature Review
• Materials and Methods 1. Material
• Test Results
• Result Discussion and Conclusions

The model is created after estimating the study population parameters' distributions, based on the observed results. Then a correlation analysis of the coefficient of permeability in terms of all physical parameters was performed. An analysis of the normality of the residual distribution (Figure 6a) and the distribution of the observed values ​​in relation to the predicted (Figure 6b) was prepared.

The correctness of the model (equation (6)) was supported by the plot of the normality of the residual distribution (Figure 8a) and the distribution of observed values ​​relative to predicted values ​​(Figure 8b). a) (b) Figure 8. Normality plot of residuals (a) and values ​​observed versus predicted (b).

Figure 1. Grain size distribution curve of each tested RCA blends.

Properties of Mortar with Recycled Aggregates, and Polyacrylonitrile Microfibers Synthesized

Some of the fibers used as reinforcement of cementitious materials include polypropylene fibers [32], polyethylene terephthalate (PET) fibers [33], polyvinyl alcohol (PVA) fibers [34], but few studies have been done with polyacrylonitrile (PAN) reinforcing fibers [35]. Table 1 shows the properties of the materials used in the production of mortars. Figure 2 shows the characterizations that were made on the PAN microfibers obtained by electrospinning and the results after separation by the homogenization process.

On the other hand, the morphology of microfibers can be observed through SEM images and using “ImageJ”.

Figure 1. Granulometry of NFA and RFA following the ASTM C-33 standard.

The absorption and resistance to water penetration are important indicators of the durability of hardened mortar. By reducing the porosity of the mortars using PAN microfibers, the capillary absorption decreased by 23.3% and the resistance to water penetration increased by 25%. Mechanical properties of concrete produced with recycled coarse aggregate—influence of the use of superplasticizers.Constr.

Experimental characterization of the response after cracking in hybrid steel/polypropylene fiber reinforced concrete.Constr.

Figure 3. Mechanical properties of mortars: (a) compressive strength and (b) flexural strength.

Numerical Studies on Damage Behavior of Recycled Aggregate Concrete Based on a 3D Model

• Basic Formula of 3D Base Force Theory
• BFEM Model of Hexahedron Element
• Random Model of RAC 1. Aggregate Number
• Simulation of Uniaxial Compressive Test
• Conclusions

The physical properties of the recycled aggregate depend on the percentage and properties of the adhesive mortar. These results can be attributed to the lower mechanical properties of the bonded mortar compared to the new cement mortar and aggregate. These phenomena can be attributed to the poorer properties of ITZ and the adhesion of mortar materials to other media.

The effects of the replacement ratio of the recycled aggregate and the percentage of adhesive mortar on the modulus of elasticity and compressive strength were investigated.

Figure 1. Base forces.

Feasible Use of Cathode Ray Tube Glass (CRT) and Recycled Aggregates as Unbound and Cement-Treated

Experimental Methods and Results 1. Modified Proctor (UNE 103501:1994) [40]

The deformation will depend on the tension and physical-mechanical properties of the terrain. The purpose of this test is to determine the simple compressive strength of materials treated with hydraulic connectors. Influence of sulfate content of recycled aggregates on the properties of cement-treated granular materials using sulfate-resistant Portland cement.

Panangikeddeng ti UN ti friability coefficient ti darat; Kappon ti Espaniol para iti Standardisasion (AENOR): Madrid, Espania, 2018.

Figure 4. Moisture–density relationship.

Recycling Aggregates for Self-Compacting Concrete Production: A Feasible Option

The production of concrete with recycled materials has been one of the most studied applications. The use of recycled materials in the production of self-compacting concrete has been gradually increasing due to the economic and environmental benefits derived from the fusion of the two techniques. Experimental study of the variation of the main mechanical properties of concrete produced with coarse recycled concrete aggregate.

The influence of the amount of mixed recycled aggregates on the properties of concrete for non-structural use. Construction.

Figure 1. Research sequence.

Study on the Microstructure of the New Paste of Recycled Aggregate Self-Compacting Concrete

Consequently, this work proposes a sampling method to study the microstructure of the new paste (NP) of self-compacting concrete (SCC) for different levels of recycled aggregates (RA). For this, SEM observations were carried out to investigate the microstructure of the new paste. The content of the anhydrous granules (white elements in Figure 8) in the new paste changes from one concrete to the next.

The volume of coarse aggregates (>3 mm) is 31% of the total volume of concrete (see table 3).

Mechanical Behavior of Masonry Mortars Made with Recycled Mortar Aggregate

Materials and Methods 1. Obtaining Recycled Aggregates

The RFAs used in this research were obtained from the renovation of the second floor of "K". The demolition of the second wall proceeded according to the developer's original plan (conventional demolition). Because the ground floor of the building was empty due to the renovation work, it was used as a CDW warehouse.

The cement used is of the brand PCC 30R type Cemex® (Monterrey, Mexico), referring to a resistance class 30 Portland cement compound with rapid resistance (3 days).

Results and Discussion 1. Deconstruction Process Effect

On the other hand, the mixtures of the RFA*+w and RFA*+P families proved to have the lowest values ​​of air content because they reduce the amount of water in the cement mass. Figures 2 and 3 clearly show the influence of the W/C ratio on the bulk density and air content of fresh mortar [19,40,61]. It is found that the control mortar (NS) develops a higher density than the mortars from the RFA* and RFA families.

Mixes made with pre-wetting aggregates (RFA*+h) showed higher resistance for each degree of replacement than RFA*.

Use of Mining Waste to Produce

Ultra-High-Performance Fibre-Reinforced Concrete

Experimental Study

As a substitute for the finest fraction of the sand, waste mine sand (WMS) (Minersa, Ribadesella, Spain) was used, which is generated in the process of obtaining fluoride or fluorite spar in fluorite mines (Figure 1a,b). The percentages of Al2O3 and Fe2O3 are approx. 1.5%, higher than for 0-0.5 mm silica sand. A difference can be seen between the granulometry of the 0-0.3 mm WMS and the fraction of 0-0.5 mm silica sand that it replaces.

All values, except for the drop, correspond to the average value of the three results obtained in each of the performed tests.

Analysis of Results

There is an increase in strength for all substitution degrees, as shown in Figure 6. These increases in concrete compressive strength are consistent with the results obtained by Zegardlo, [11] who obtained a 24.7% increase in strength using ceramic waste as an alternative to natural aggregate. He attributes this improvement to the formation of mechanical hooks in the interfacial transition zone (ITZ), which generate better adhesion with the cement paste and greater strength.

Similar results were obtained by Zhu [7], who observed an increase in compressive strength by incorporating 0–1.20 mm iron ore tailings to replace 0–4.75 mm silicate sand, independent of the replacement percentage.

Elasticity Modulus

Equation (1) represents the value of the modulus of elasticity (E) as a function of the slope (m) of the elastic region of the stress-strain curve and the thickness (h) of the sample in mm. This variation may be due to the random distribution of the fibers in UHPFRC. The possible explanation, as in the bending strength, is the inferior quality of the mine sand used.

The density of UHPFRC with WMS is very similar to that of the control concrete.

Complete Real-Scale Application of Recycled Aggregates in a Port Loading Platform

Research Design

Execution of the loading platform at the Port of Huelva, specified in Figure 1, applying MRA and RCA to the base and sub-base structural layers of the platform. At this stage, the density and water absorption of both granular structural layers of the loading platform were determined to confirm the correct application of MRA and RCA. This allowed the survey of the area in a longitudinal direction, obtaining an equivalent extension of 1750 m in length.

After the execution of the application, and with a defined frequency, the basic parameters were evaluated.

Recycled Materials