Modified Fine Recycled Concrete Aggregates with a Crystallizing Agent as Standard Sand Replacement in Mortar
Abstract
1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Methods
2.2.1. Sieving Process
2.2.2. Recycled Sand Characterization
2.2.3. Mortar Samples Preparation
2.3. Mortar’s Characterization
2.3.1. Mechanical Behavior
2.3.2. Chloride Permeability Test
2.3.3. Water Penetration Resistance
3. Results
3.1. Recycled Sand Characterization
3.1.1. Thermogravimetric Analysis (TGA)
3.1.2. Field Emission Scanning Electron Microscopy (FESEM) Observations
3.1.3. X-Ray Diffraction and X-Ray Fluorescence (XRD and XRF)
3.2. Mechanical Behavior
3.2.1. CON Series
3.2.2. CON-X Series
3.2.3. CON-Y Series
3.2.4. CON-Z Series
3.3. Chloride Permeability Test
3.4. Water Penetration Resistance
4. Conclusions
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
AD | Admixplus |
CA | Crystalline admixture |
CDW | Construction and demolition waste |
DE | Diatomaceous earth |
FA | Fly ash |
ITZ | Interfacial transition zone |
LE | Linear economy |
MICP | Microbial induced carbonate precipitation |
NA | Natural aggregate |
NS | Nano-silica |
OPC | Ordinary Portland cement |
RA | Recycled aggregate |
RCA | Recycled concrete aggregate |
RCPI | Rapid chloride permeability index |
RFA | Recycled fine aggregate |
RS | Recycled sand |
SF | Silica fume |
SP | Superplasticizer |
SS | Standard sand |
TBP | Three-point bending |
W:c | Water to cement ratio |
WG | Waterglass |
WGP | Waste glass powder |
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Square Mesh Size [mm] | Cumulative Retained [%] | Retained [%] | Retained Mass [g] |
---|---|---|---|
2.00 | 0.0 | 0.0 | 0.0 |
1.60 | 7.0 | 7.0 | 94.5 |
1.00 | 33.0 | 26.0 | 351.0 |
0.50 | 67.0 | 34.0 | 459.0 |
0.16 | 87.0 | 20.0 | 270.0 |
0.08 | 99.0 | 12.0 | 162.0 |
Filler | 100.0 | 1.0 | 13.5 |
Density of Particles [g/cm3] | Purity | Water Absorption [%] | |
---|---|---|---|
Powders Content | Sand Equivalent [%] | ||
2.46 | f22 | 48 | 4.73 |
Size [mm] | CON 25% | CON 50% | CON 75% | CON 100% | ||||
---|---|---|---|---|---|---|---|---|
SS [g] | RA [g] | SS [g] | RA [g] | SS [g] | RA [g] | SS [g] | RA [g] | |
1.6 | 70.90 | 23.60 | 47.30 | 47.30 | 23.60 | 70.90 | 0.00 | 94.50 |
1.0 | 263.30 | 87.80 | 175.50 | 175.50 | 87.80 | 263.30 | 0.00 | 351.00 |
0.5 | 344.30 | 114.80 | 229.50 | 229.50 | 114.80 | 344.30 | 0.00 | 459.00 |
0.16 | 202.50 | 67.50 | 135.00 | 135.00 | 67.50 | 202.50 | 0.00 | 270.00 |
0.08 | 121.50 | 40.50 | 81.00 | 81.00 | 40.50 | 121.50 | 0.00 | 162.00 |
Filler | 10.10 | 3.40 | 6.75 | 6.75 | 3.40 | 10.10 | 0.00 | 13.50 |
Total | 1350.00 | 1350.00 | 1350.00 | 1350.00 |
Series | Specimen ID | W/C | Cement [g] | Water [g] | Sand | SP [%] | AD [g] | |
---|---|---|---|---|---|---|---|---|
SS [g] | RS [g] | |||||||
1 | OPC | 0.50 | 450.00 | 225.00 | 1350.00 | 0.25 | - | |
CON 25 | 0.50 | 450.00 | 225.00 | 1012.50 | 337.50 | 1.25 | - | |
CON 50 | 0.50 | 450.00 | 225.00 | 675.00 | 675.00 | 1.70 | - | |
CON 75 | 0.50 | 450.00 | 225.00 | 337.50 | 1012.50 | 2.80 | - | |
CON 100 | 0.50 | 450.00 | 225.00 | - | 1350.00 | 5.00 | - | |
2 | OPC-X | 0.50 | 450.00 | 225.00 | 1350.00 | - | 0.25 | 4.50 |
CON-X 25 | 0.50 | 450.00 | 225.00 | 1012.50 | 337.50 | 1.25 | 4.50 | |
CON-X 50 | 0.50 | 450.00 | 225.00 | 675.00 | 675.00 | 1.70 | 4.50 | |
CON-X 75 | 0.50 | 450.00 | 225.00 | 337.50 | 1012.50 | 2.80 | 4.50 | |
CON-X 100 | 0.50 | 450.00 | 225.00 | - | 1350.00 | 5.00 | 4.50 | |
3&4 | ||||||||
OPC-Y/Z | 0.50 | 450.00 | 225.00 | 1350.00 | - | 0.10 | 13.50 | |
CON-Y/Z 25 | 0.50 | 450.00 | 223.45 | 1012.50 | 337.50 | 2.00 | 13.50 | |
CON-Y/Z 50 | 0.50 | 450.00 | 213.40 | 675.00 | 675.00 | 3.10 | 13.50 | |
CON-Y/Z 75 | 0.50 | 450.00 | 200.85 | 337.50 | 1012.50 | 4.90 | 13.50 | |
CON-Y/Z 100 | 0.50 | 450.00 | 188.30 | - | 1350.00 | 7.10 | 13.50 |
Series | Specimen ID | Slump [mm] |
---|---|---|
1 | OPC | 36 |
CON 25 | 35 | |
CON 50 | 35 | |
CON 75 | 36 | |
CON 100 | 32 | |
2 | OPC-X | 43 |
CON-X 25 | 45 | |
CON-X 50 | 44 | |
CON-X 75 | 44 | |
CON-X 100 | 45 | |
3 | OPC-Y | 42 |
CON-Y 25 | 40 | |
CON-Y 50 | 42 | |
CON-Y 75 | 40 | |
CON-Y 100 | 43 | |
4 | OPC-Z | 42 |
CON-Z 25 | 40 | |
CON-Z 50 | 42 | |
CON-Z 75 | 40 | |
CON-Z 100 | 43 |
Component | Mass% |
---|---|
LOI-Flux | 12.000 |
Na2O | 1.380 |
MgO | 4.750 |
Al2O3 | 9.100 |
SiO2 | 42.800 |
P2O5 | 0.157 |
SO3 | 3.420 |
Cl | 0.079 |
K2O | 1.730 |
CaO | 19.300 |
TiO2 | 0.392 |
Cr2O3 | 0.067 |
MnO | 0.169 |
Fe2O3 | 4.490 |
NiO | 0.033 |
CuO | 0.011 |
ZnO | 0.017 |
As2O3 | 0.009 |
Rb2O | 0.010 |
SrO | 0.037 |
Y2O3 | 0.002 |
ZrO2 | 0.035 |
Aggregates’ Treatment | Water Absorption or Porosity | Mechanical Strength | Ref. |
---|---|---|---|
Enzyme-induced carbonate precipitation (EICP) modified RAs | 7.01% water absorption reduction with respect to untreated RA | 6.05% increase in concrete’s compressive strength with respect to untreated RAs (50.85 MPa, w:c = 0.39, 100% replacement rate) | [61] |
Nano-silica (NS) solution (2 wt%) immersion + carbonation treatment modified RCAs | 5.13% water absorption for hydrophobic NS treated and carbonated RAs (1.42% for natural aggregates) | 34.9% increase in concrete’s compressive strength with respect to untreated RAs (40.29 MPa, w:c = 0.46, 50% replacement rate) | [62] |
Soaked 3% bacterial liquid + 0.1 mol/L calcium acetate and 20% CO2 carbonation modified RAs | After 50 freeze–thaw cycles, the mass loss of concrete made with treated aggregates was 0.49%, while that of concrete made with untreated aggregates was 4.99% | 32% increase in concrete’s compressive strength with respect to untreated RAs (31.48 MPa, w:c = 0.6, 100% replacement rate) | [63] |
Bacillus cereus modified coarse aggregates | 40% reduction in water absorption for treated coarse aggregates with respect to untreated ones | Same compressive strength resistance as concrete made with NA. 11% higher split tensile strength (39.59 MPa, w:c = 0.44, 40% replacement rate) | [33] |
Pozzolan (silica fume, fly ash, nano-silica) slurry impregnation or carbonation of coarse aggregates | 3.9–4.2% water absorption for treaded aggregates against 5.3% for untreated ones | Up to 55.2% increase in compressive strength for silica fume treated mortar (w:binder = 0.5 and RCA:binder = 2.5) | [64] |
Microbial-induced carbonate precipitation (MICP)-modified fine aggregates | 50.47% reduction in water absorption after 4 cycles of modification | Flexural strength of mortar made with modified aggregates increased by 23.3% compared to untreated one (w:c = 0.5) | [65] |
NS soaking + carbonation | Sulfate penetration depth reduced by over 30% for modified RAs compared to untreated ones | Compressive strength of NS-modified RAs after 28 days of sulfate attack increased by 15% with respect to unmodified RA | [66] |
Calcium carbonate precipitation from urea and calcium acetate upon heating | 32% water absorption reduction for soaked RAs kept at 80 °C for 5 days with respect to untreated RA | Compressive strength of concrete decreased by 2.2%, 3.5%, 8.4%, and 10.2% for replacement ratios of 30%, 50%, 70%, and 100%, respectively, compared to control made with NAs | [67] |
MICP-modified coarse aggregates | Up to 17.9% reduction in water absorption for treated aggregates with respect to untreated ones | 17.7% increase in compressive strength compared to untreated aggregates (w:c = 0.5, 100% coarse aggregates replacement) | [68] |
Carbonation + coating with an alkali-activated fly ash–slag slurry | Up to 31.43% reduction in water absorption for aggregates first carbonated under 20% CO2 and 70 RH%, then impregnated with a saturated lime solution | 58.6% increase in concrete’s compressive strength (45.68 MPa) | [69] |
Carbonation of coarse RA | 5.4–7.1% water absorption for treated RAs with respect to 6.8–8.4% for untreated RA. Coarser RA (10–20 mm) absorbed less water than smaller RA (5–10 mm). | 10.5% increase in compressive strength for concrete made with treated RAs compared to the one made with untreated RA; only ≈80% of compressive strength with respect to concrete made with NAs (w:c = 0.38 for NA, w:c = 0.5 for treated RA, 100% replacement) | [70] |
RA pre-soaked in 5% silane emulsion | 65.2% water absorption reduction | Increase in average flexural fatigue life by 28.5, 36.9, and 44.2 times at the stress levels of 0.6, 0.7, and 0.8 after 140 freeze–thaw cycles (w:c = 0.5, 100% replacement) | [71] |
Pre-impregnation or pre-spraying of RAs with calcium phosphate (CaP) solutions | When CaP to RA was 0.003 g/g, the water absorption of pre-sprayed and pre-impregnated treated RAs was 18.02% and 21.61% lower than that of untreated RA, respectively. | When the ratio of CaP to RA was 0.001 g/g, compressive strength increased by 31.52% with pre-spray treatment (100% replacement). In samples with 50% RA and 50% NA, when the unit weight ratio of CaP to RA was 0.003 g/g, the compressive strength increased by 16.52% with pre-impregnation (w:c = 0.35 in all tests). | [72] |
Accelerated carbonation (101 kPa, 99.99%, 24 h) and NS solution (2%) immersion | 26.4% reduction in water absorption | n.e. | [73] |
Accelerated carbonation (150 kPa, 99.9%, 72 h) | 23.3% water absorption reduction for treated aggregates (4.86%) compared to non-treated ones (6.34%) (NA = 0.8%) | 14.3% and 22.1% decrease in compressive strength and elastic modulus, respectively, with respect to NAs (w:c = 0.53, 100% replacement of coarse aggregates) | [74] |
Immersion in a slurry with 15% fly ash, 3% gypsum, and 22% polyacrylate emulsion for 180 s | Saturated surface–dry water absorption rate decreased from 15.0% to 9.5% for treated aggregates with respect to untreated ones | 54.5% increase in compressive strength (w:c = 0.4, 100% replacement of coarse aggregates) | [75] |
Vacuum impregnation with a 4% NS slurry | 2.81% porosity for treated aggregates compared to 4.2% for untreated aggregates (estimated by X-CT) | 18.39% increase in compressive strength compared to non-treated aggregates: 55.97 and 47.3 MPa, respectively (w:c = 0.45, 100% replacement of coarse aggregates; 57.9 MPa for the concrete made with NA) | [76] |
Impregnation with a 3% NS solution | 36.96% porosity reduction with a decrease of 14.35% of average pore size for treated aggregates with respect to untreated ones | 41.68 MPa and 34.56 MPa, 52.35 MPa and 44.16 MPa, and 63.22 MPa and 54.25 MPa for treated and untreated aggregates (100% replacement of coarse aggregates) for w:c = 0.51, 0.41, and 0.36, respectively | [77] |
Soaking in cement fly ash slurries (30% and 70% concentration) | 5.4% water absorption for 24 h soaked aggregates in a 70% concentrated solution compared to 8.7% for untreated aggregates | n.e. | [78] |
Accelerated carbonation (20%) of coarse aggregates | The water absorption of carbonated aggregates was reduced by 19.16%, 21.8%, and 16.3%, for the fractions 5–10 mm, 10–20 mm and 20–25 mm, respectively | n.e. | [79] |
Sodium alginate microbial induced calcium carbonate precipitation on RA | 32.85% decrease in water absorption after CaCO3 precipitation | n.e. | [80] |
Accelerated carbonation (20%) of coarse aggregates from different concrete strength classes (C30, C40, and C50) | Up to 20% reduction in water absorption for carbonated RAs from C50-strength concrete (5–10, 10–20, and 20–25 mm) compared to non-treated aggregates | n.e. | [81] |
RCAs incorporating air-entraining agents (AEAs) and nano-silica solution (30 wt%) | n.e. | 56.4 MPa, 42.7 MPa and 32.9 MPa for 0, 50 and 100% coarse aggregates replacement with 0.05% of AEA (w:c = 0.4) | [82] |
RA first immersed in a slurry with a water-to-binder ratio of 0.8, in which 20% of the OPC (ordinary Portland cement) was replaced by FA (fly ash) and SF (silica fume). Next, the coated RAs were immersed in sodium silicate (waterglass, WG) and silicon-based additive solutions | Compared with untreated aggregates, the total pore volume of C30 concrete with RAs with WG and SA decreased by 30.3% and 32.9%, while the average pore diameter decreased by 12.5% and 24.7%, respectively | When the replacement rate of RAs is 50% and 100%, the compressive strengths of recycled concrete with the strength grade of C30 are 36.0 and 29.6 MPa, 15.1% and 30.2% lower than that of the ordinary concrete, respectively. | [83] |
Pre-soaked or pre-sprayed RAs in a graphene oxide (GO) solution (0, 0.01, 0.03, and 0.05 wt% of GO with respect to cement) | Compared with untreated aggregates, the total porosity of RAs pre-soaked in a solution with 0.05 wt% of GO decreased by 27.8%. The detrimental pores with an equivalent diameter larger than 50 nm was reduced by 35.5%. | Compressive strength increased by 8.3%, 18.1%, and 30.8% at 7 days, and 9.5%, 14.4% and 23.5% at 90 days, for RAs pre-soaked in a solution with 0.01, 0.03, and 0.05 wt% of GO, respectively, compared to untreated aggregates. With 5 wt% addition of GO, the compressive strength was very close to that of concrete made with NAs (w–binder = 0.55, 100% coarse aggregates replacement). | [84] |
Bio-deposition of biogenic silica by means of diatoms | Hydrophobicity close to that observed in nano-silica (50 nm) coatings (50 wt%) | Increase in the compressive strength up to 8% in function of the diatoms’ growth conditions (indoor or outdoor) compared to non-treated aggregates (w:c = 0.59, 50% coarse aggregates replacement) | [85] |
Immersion in 2, 5, 10 and 30 wt% NS solutions for 24 h of RA (5–10 and 10–20 mm) | Compared to untreated RA, the water absorption of RAs treated with 2%, 5%, 10%, and 30% NS solution decreased by 18.2%, 21.1%, 22.6%, and 27.6%, respectively; 2% concentration of NS solution is sufficient to consume portlandite of RA | The compressive strengths of concrete made with RAs treated with NS solutions at different concentrations (2%, 5%, 10%, and 30%) were, respectively, 14.5%, 17.2%, 25.9%, and 28.8% higher compared to the concrete manufactured with untreated RA. Further improvement of 5.4%, 6.4%, 5.1%, and 6.9%, respectively, if excess NS not removed from the surface | [86] |
Soaking in 3% bacterial solution and 0.1 mol/L calcium acetate solution followed by carbonation with 20% CO2 (101 kPa) | 4.72% water absorption for the 3% concentrated bacterial solution, compared to 9% for untreated aggregates | n.e. | [87] |
MICP based on hydrolyzing urea (best results when the ratio of bacterial solution concentration to urea concentration = 5) | 10% decrease in water absorption for treated aggregates with respect to untreated ones | 48 MPa compressive strength for the concrete made with treated aggregates (+19.5% with respect to concrete made with untreated aggregates) (w:c = 0.49, 100% coarse aggregates replacement) | [88] |
RA soaking in slurries based on OPC and diatomaceous earth (DE) ((OPC + DE):water = 1:2 by weight) | Increase in water absorption with increase in DE in the slurry (up to 20%): from 2.32% for untreated aggregates to 5.15% for 20%DE slurry | 20% increase in compressive strength for the concrete with the aggregates soaked in the slurry with 5% DE, with respect to non-treated aggregates (w:c = 0.5, 100% coarse aggregates replacement) | [89] |
Carbonation of coarse RA (20% CO2) from C40-strength concrete | 16.3–21.8% lower water absorption for carbonated aggregates in function of their size (5–10, 10–20, and 20–25 mm). About +160% water absorption with respect to natural aggregates with the same size | The average compressive strength of concrete made with carbonated RAs was 52.47 MPa, compared to 54.37 MPa for the concrete manufactured with natural aggregates and 47.43 MPa for samples with non-treated RAs (w:c = 0.4, 100% coarse aggregates replacement) | [90] |
Immersion of coarse RA in an 8% solution of sodium silicate and a 12% solution of silane | 8.12% water absorption for RA, compared to 3.83% for treated RA | Compressive strength of concrete made with impregnated RAs increased from 33.75 to 38.09 MPa (+12.86%) with respect to that made of pristine RAs (w:c = 0.5) | [91] |
Presoaking for 24 h in a 1.5 wt% NS solution combined with carbonation (99%, 300 kPa) of coarse RA | About 22% reduction in water absorption for treated RA. Limited variations in function of the studied fractions (4.75–7, 7.5–9, and 9.5–12 mm) | Compared to cast samples, the loss ranges in compressive strength of printed specimens were 15.37–19.41% in the X direction, 21.61–25.62% in the Y direction, and 28.65–33.04% in the Z direction, in function of the replacement rates (30, 70, and 100%) (w:c = 0.41–0.61, higher for higher replacement rates) | [92] |
Carbonation (20% CO2) of RFA in 0.5 M and 1.0 M NaOH solutions | 9.1% for fine RAs carbonated at 0.5 M-45 °C, with respect to 10.1% for pristine RA | Mortars prepared with RFAs carbonated at 0.5 M-45 °C for 10 min acquired comparable strength to the reference mortar prepared with RFAs carbonated at 25 °C for 6 h in absence of NaOH. The highest compressive strength was 48.8 MPa, corresponding to an increase of 17.0% with respect to the mortar made with natural sand (binder–water = 0.5, 100% replacement of RFAs) | [93] |
Immersion of coarse RA in a commercial crystallizing agent solution for 1 day or 7 days | 24.82% water absorption reduction after 1 day of immersion, 58.49% water absorption reduction after 7 days of immersion | 46.9 MPa compressive strength for concrete made with 7 days immersed RA, compared to 47.7 MPa for concrete made with NAs (w:c = 0.4, 100% coarse aggregates replacement) | [47] |
Immersion of coarse RA (5–10 and 10–25 mm) in a commercial crystalline admixture (CA) solution with waste glass powder (WGP) | Whatever the WGP content, the CA controls the water absorption (≈0.25–0.5% after 11 days) | The compressive strength of the samples decreased with the increasing WGP content, whatever the CA content (1 or 2%) (w–binder = 0.53, 100% coarse aggregates replacement) | [48] |
Immersion of RFAs in a commercial crystallizing agent solution | Water penetration under pressure = 6 mm for mortar made with SS, while mortar made with treated RFAs (cured for 15 days) showed a penetration of 9 mm | About 65 MPa compressive strength for 100% replacement of fine aggregates with treated RFAs (CON-Y, cured 15 days), compared to about 55 MPa for mortars made with standard sand | This work |
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Suarez-Riera, D.; Lavagna, L.; Falliano, D.; Ferro, G.A.; Pavese, M.; Tulliani, J.-M.; Restuccia, L. Modified Fine Recycled Concrete Aggregates with a Crystallizing Agent as Standard Sand Replacement in Mortar. Materials 2025, 18, 4208. https://doi.org/10.3390/ma18174208
Suarez-Riera D, Lavagna L, Falliano D, Ferro GA, Pavese M, Tulliani J-M, Restuccia L. Modified Fine Recycled Concrete Aggregates with a Crystallizing Agent as Standard Sand Replacement in Mortar. Materials. 2025; 18(17):4208. https://doi.org/10.3390/ma18174208
Chicago/Turabian StyleSuarez-Riera, Daniel, Luca Lavagna, Devid Falliano, Giuseppe Andrea Ferro, Matteo Pavese, Jean-Marc Tulliani, and Luciana Restuccia. 2025. "Modified Fine Recycled Concrete Aggregates with a Crystallizing Agent as Standard Sand Replacement in Mortar" Materials 18, no. 17: 4208. https://doi.org/10.3390/ma18174208
APA StyleSuarez-Riera, D., Lavagna, L., Falliano, D., Ferro, G. A., Pavese, M., Tulliani, J.-M., & Restuccia, L. (2025). Modified Fine Recycled Concrete Aggregates with a Crystallizing Agent as Standard Sand Replacement in Mortar. Materials, 18(17), 4208. https://doi.org/10.3390/ma18174208