Specimens were prepared by altering parameters such as aggregate sizes, binder materials, and the amounts of binder used and were subsequently tested by using permeability, porosity, mechanical strength, and soundness tests. The results indicated that the water permeability coefficient and connected porosity decreased as the amount of binder used increased and increased with increasing aggregate size. In the mechanical strength test, the compressive, splitting tensile, and flexural strengths increased as the amount of binder used increased and decreased with the increase of aggregate size. Highly viscous binder enhanced compressive strength, water permeability, and the resistance to sulfate attacks. In the mechanics and sulfate soundness tests, the mix proportion of alkali-activated slag paste used in this study exhibited a superior performance than the Portland cement pervious concrete (the control) did, but the difference in water permeability between the two types of concrete was insignificant. The mix proportions of cement paste containing 20% and 30% silica fume exhibited less mechanical strength than the control did. Moreover, compared with the control, the cement paste containing silica fume demonstrated poor resistance to sulfate attacks, and the difference in the water permeability between such specimen and the control was not noticeable.
Pervious concrete, also known as no-fines concrete, is a type of porous composite material that can be regarded as concrete composed of minimal to fine uniformly graded aggregates and a limited amount of cement paste. Because of its pervious properties, the pervious concrete pavement provides a better temperature and humidity exchange between atmosphere and earth than the impervious pavement such that the so-called “heat-island” effect in the urban region can be reduced. In addition, pervious concrete is regarded as a remedy for the flood control due to its excellent water permeability. Also, it is known that the pervious concrete pavement reduces traffic noise and has an excellent antiskid performance.
However, a lower mechanical strength of pervious concrete constrains the application of pervious concrete. Due to the porosity inside the pervious concrete, its compressive strength does not satisfy the minimal requirement for the structural concrete (21 MPa for 28-day compressive strength). Therefore, most applications for pervious concrete are parking lot pavement, pedestrian walkway, bike route, and places where concrete compressive strength is not important. In the following, literature survey for pervious concrete is given.
Generally, because of the high amount of connected voids in pervious concrete, compressive strength is relatively low; thus, the strength of pervious concrete can be improved using the following strategies [ enhancing the characteristics of binder by decreasing the water-cement (w/c) ratio and adding pozzolanic materials such as silica fume; adopting different binder materials such as using epoxy to replace cement pastes; applying slight pressure and increasing the temperature in the curing stage.
Marolf et al. studied the effect of aggregate size and gradation on the acoustic absorption for pervious concrete. They reported that pervious concrete mixtures with single-sized aggregates provide substantial improvement to sound absorption as compared with conventional concrete [
Park and Tia studied water purification effect of pervious concrete. They found that a porous concrete with a smaller size of aggregate and a higher void content was found to have superior ability of the removal of the total phosphorus and total nitrogen in the test water. They concluded that this effect is due to the large specific surface area of the porous concrete [
Neithalath et al. used the values of porosity and the morphologically determined pore sizes, along with the pore phase connectivity represented using an electrical conductivity ratio, in a Katz-Thompson type relationship to predict the permeability of pervious concretes [
Putman and Neptune evaluated different pervious concrete test specimen preparation techniques in an effort to produce specimens having properties similar to in-place pervious concrete pavement [
In this study, the performance of pervious concrete was investigated by conducting various tests (i.e., mechanical, permeability, soundness, porosity, and unit weight tests) by changing parameters, which include aggregate size and the type, amount, and w/c ratio of binders (for filling the voids among aggregates). However, in addition to featuring excellent water permeability, pervious concrete is expected to exhibit a mechanical performance to a certain level. Generally, once pervious concrete has excellent water permeability then its strength becomes poor. Various strategies can be used to improve the strength of pervious concrete while achieving the required permeability. By altering the parameters of pervious concrete, this study obtained the optimal relationship between strength and water permeability. Subsequently, the required mix proportion was attained through relevant analyses, and different binders were applied to multiple types of pervious concrete to determine the mechanical characteristics and water permeability of pervious concrete. In the experiment, the control group comprised pure cement paste as binding material, and the experiment group involved two types of cement pastes, one containing silica fume and one with alkali-activated slag. The feasibility of enhancing mechanical strength or changes in water permeability can be investigated using different binders.
The experiment involved two stages. The first part involved considering three crucial parameters, which were aggregate size, the volume percent of aggregate voids filled with binders, and the w/c ratio of binders, for determining the relationship between water permeability and mechanical strength. Next, the feasibility of enhancing mechanical strength was determined by varying the types of binders used based on the mix proportions obtained from the first part of the experiment. The second stage was aimed at investigating cement pastes containing silica fume and alkali-activated slag. Varying amounts of silica fume were used to replace cement; in other words, cement combined with pozzolanic material was used instead of pure cement paste. Alkaline-activated slag paste with different liquid/slag (L/Sg) ratios was used to replace the pure cement pastes. Finally, the experiment and control (pure cement paste only) groups were compared to investigate the influences of different binding materials on the properties of pervious cement.
Pervious concrete is primarily composed of aggregates and binding materials, which bind aggregates and fill voids among aggregates to form porous, permeable concrete. Regarding applications in engineering, pervious concrete should have a certain level of water permeability before its mechanical strength is enhanced. Therefore, designing the void content inside pervious concrete is the key that affects the overall property of the material. High porosity in pervious concrete indicates excellent water permeability but poor mechanical strength because of insufficient compactness. By contrast, low porosity can enhance mechanical strength but might decrease water permeability. Although such judgment can be preliminarily made based on physics concepts, when variables such as binder characteristics and aggregate size are considered, whether or not the effect of porosity on the property of previous concrete conforms to common concepts must be determined by experimental studies. The parameter design concepts are explained as follows. Aggregate size: in this experiment, uniformly graded aggregates (narrow gradation) were used, which are aggregates of a single size. In addition, aggregate size affects the water permeability and mechanical strength of pervious concrete. W/c ratio: in pervious concrete, when designing the w/c ratios of cement pastes, workability, water permeability, and mechanical strength should be considered. The workability of cement pastes influences the overall performance of pervious concrete. The volume percent of aggregate voids filled with binders (hereafter referred to as volume percent of filled voids): this volume percent refers to the amount of binders used in pervious concrete. This amount also influences the water permeability and mechanical strength of pervious concrete. Binders: mechanical strength is enhanced by altering binders, which influence the property of pervious concrete.
The binders used in the first stage were cement pastes made by mixing cement with water. Superplasticizers were added to the binder with a low w/c ratio of 0.25 to increase the binder fluidity. In the second stage, cement pastes containing silica fume and alkali-activated slag were used. Based on the first stage of the experiment, the control group involved the following parameters: B aggregate size, w/c ratio of 0.35, and 80% volume percent of filled voids. Subsequently, comparison test was conducted in which the mix proportion of binders was altered. The experimental variables are shown in Table
Experimental variables of the two-stage experiment.
Experimental variables of Stage 1 | ||||
|
||||
Aggregate code and size | A |
B |
C |
D |
Binder | Cement paste | |||
w/c ratio | 0.25 0.35 0.452 | |||
Total volume percent of filled voids | 50% | 60% | 70% | 80% |
Aggregate code and size | B (0.48 cm) |
Experimental variables of Stage 2 | ||
|
||
Binder | Alkali-activated slag paste | Silica-fume cement paste |
Total volume percent of filled voids | 80% | |
L/Sg or w/c ratio | 0.35 0.4 0.45 | 0.35 |
Substitution ratio | — | 10% 20% 30% |
This study used the Portland Type I cement produced and coarse aggregates of four different sizes as those in Table
Physical properties of coarse aggregates.
Code | A | B | C | D |
Nominal size | 1/8 in. | 3/16 in. | 1/4 in. | 3/8 in. |
Maximum size | 0.48 cm | 0.64 cm | 0.95 cm | 1.27 cm |
Range of particle sizes | 0.24–0.48 cm | 0.48–0.64 cm | 0.64–0.95 cm | 0.95–1.27 cm |
Specific gravity | 2.65 | 2.69 | 2.66 | 2.72 |
Void volume per unit volume | 37.3% | 37.5% | 36.8% | 38.3% |
Superplasticizers are high-performance carboxylic plasticizers. The chemical compositions of sodium silicate, sodium hydroxide, and phosphoric acid used for making alkali-activated slag paste are shown in Tables
Chemical composition of sodium silicate.
Item | Sodium silicate |
|
|
Test item | Test result |
|
|
Insoluble residue | Max. 0.01% |
Silicon dioxide (%) | 37.0% |
Sodium oxide (%) | 17.7% |
Mole ratio | 2.16 |
Iron (Fe) | Max. 0.02% |
Chemical composition of sodium hydroxide.
Test item | Test results |
|
|
Chloride (Cl) | Max. 0.005% |
Sulfate (SO4) | Max. 0.003% |
Silicate (SiO2) | Max. 0.01% |
Phosphate (PO4) | Max. 0.001% |
Heavy metals (arsenic and lead) | Max. 0.001% |
Iron (Fe) | Max. 0.0007% |
Aluminum (Al) | Max. 0.003% |
Calcium (Ca) | Max. 0.001% |
Magnesium (Mg) | Max. 0.0005% |
Potassium (K) | Max. 0.1% |
Total nitrogen (N) | Max. 0.001% |
Arsenic (As) | Max. 0.0002% |
Sodium carbonate (Na2CO3) | Max. 2.0% |
Assay (NaOH) | Max. 95.0% |
Chemical composition of phosphoric acid.
Item | Phosphoric acid |
|
|
Test item | Test results |
|
|
Chloride (Cl) | Max. 0.001% |
Nitrate (NO3) | To pass test |
Sulfate (SO4) | Max. 0.006% |
Alkali and other phosphates (sulfate) | To pass test |
Substances reducing KMnO4 | To pass test |
Heavy metals (As and Pb) | Max. 0.001% |
Iron (Fe) | Max. 0.005% |
Arsenic (As) | Max. 0.0003% |
Specific gravity | 1.700–1.710 |
Assay | Max. 85.0% |
We first determined the void volume per unit volume for Types A, B, C, and D aggregates as shown in Table
Testing proportions of cement pastes as a binder.
Binder | Aggregate | W/c ratio | Percent of voids filled | Amount of aggregate (kg/m3) | Amount of cement (kg/m3) | Amount of mixing water (kg/m3) | Amount of plasticizer (kg/m3) |
---|---|---|---|---|---|---|---|
Cement paste | A | 0.25 | 50% | 1665 | 328 | 66 | 17 |
60% | 1665 | 394 | 79 | 20 | |||
70% | 1665 | 460 | 92 | 23 | |||
80% | 1665 | 525 | 105 | 26 | |||
0.35 | 50% | 1665 | 279 | 96 | — | ||
60% | 1665 | 335 | 115 | — | |||
70% | 1665 | 391 | 134 | — | |||
80% | 1665 | 447 | 154 | — | |||
0.45 | 50% | 1665 | 243 | 109 | — | ||
60% | 1665 | 291 | 131 | — | |||
70% | 1665 | 340 | 153 | — | |||
80% | 1665 | 389 | 175 | — | |||
B | 0.25 | 50% | 1684 | 330 | 66 | 17 | |
60% | 1684 | 396 | 79 | 20 | |||
70% | 1684 | 462 | 92 | 23 | |||
80% | 1684 | 568 | 106 | 26 | |||
0.35 | 50% | 1684 | 281 | 98 | — | ||
60% | 1684 | 337 | 118 | — | |||
70% | 1684 | 393 | 138 | — | |||
80% | 1684 | 449 | 157 | — | |||
0.45 | 50% | 1684 | 244 | 110 | — | ||
60% | 1684 | 293 | 132 | — | |||
70% | 1684 | 342 | 154 | — | |||
80% | 1684 | 391 | 176 | — | |||
C | 0.25 | 50% | 1683 | 324 | 65 | 16 | |
60% | 1683 | 389 | 78 | 19 | |||
70% | 1683 | 454 | 91 | 23 | |||
80% | 1683 | 518 | 104 | 26 | |||
0.35 | 50% | 1683 | 276 | 96 | — | ||
60% | 1683 | 331 | 116 | — | |||
70% | 1683 | 386 | 135 | — | |||
80% | 1683 | 441 | 154 | — | |||
0.45 | 50% | 1683 | 240 | 108 | — | ||
60% | 1683 | 288 | 129 | — | |||
70% | 1683 | 336 | 151 | — | |||
80% | 1683 | 384 | 173 | — | |||
D | 0.25 | 50% | 1682 | 337 | 67 | 17 | |
60% | 1682 | 404 | 81 | 20 | |||
70% | 1682 | 471 | 94 | 24 | |||
80% | 1682 | 530 | 108 | 27 | |||
0.35 | 50% | 1682 | 286 | 100 | — | ||
60% | 1682 | 343 | 120 | — | |||
70% | 1682 | 401 | 140 | — | |||
80% | 1682 | 458 | 160 | — | |||
0.45 | 50% | 1682 | 249 | 112 | — | ||
60% | 1682 | 299 | 134 | — | |||
70% | 1682 | 349 | 157 | — | |||
80% | 1682 | 398 | 179 | — |
The alkali activator was made by first adding sodium hydroxide to sodium silicate and then mixing the mixture uniformly before phosphoric acid (retarder) was added. The mix proportion design is shown in Table
The mix proportion of alkali-activated slag paste.
L/Sg | 0.35 | 0.40 | 0.45 |
Aggregate size | B | ||
Volume percent of filled voids | 80% | ||
Concentration of alkali activator | SiO2 = 106 g/L | Na2O = 105 g/L | |
Amount of phosphoric acid | 0.74 M | ||
Amount of slag (kg/m3) | 432 | 403 | 377 |
Amount of alkali-activated solution (kg/m3) | 151 | 161 | 170 |
Amount of aggregate (kg/m3) | 1684 | 1684 | 1684 |
Table
The mix proportion of silica-fume cement paste.
Proportion of cement replaced by silica fume | 10% | 20% | 30% |
Aggregate size | B | ||
Volume percent of filled voids | 80% | ||
Amount of cement (kg/m3) | 404 | 359 | 314 |
Amount of silica fume (kg/m3) | 39 | 78 | 118 |
Amount of mixing water (kg/m3) | 155 | 153 | 151 |
Amount of aggregate (kg/m3) | 1684 |
Porosity test: the total porosity in pervious concrete includes disconnected porosity and connected porosity, which is the primary influencing factor of water permeability. A caliper was used to measure and calculate specimen volume Unit weight: after the pervious concrete specimens solidified and were demolded, they were dried in an oven at 105 ± 5°C until their weights were stable. The specimens were weighed and analyzed using a caliper to measure, calculate, and obtain their volumes. Dividing the weight by volume yields the weight of pervious concrete per unit volume. Compressive strength: compressive strength was determined based on the ASTM C39 for cylindrical concrete specimens. Flexural strength: flexural strength was determined based on the three-point bending test. Splitting tensile strength: this test was performed for determining the splitting tensile strength of cylindrical concrete specimens. Water permeability coefficient: the water permeability coefficient was calculated using the constant-head permeability test, which is based on the Pavement Test Manual established by the Japan Road Association. The permeability instrument measured the permeability coefficient of Soundness test: aggregate soundness tests using magnesium sulfate were employed. Specimens were placed in an oven at 110 ± 5°C to dry until the constant weight
Because pervious concrete has numerous voids, its unit weight is slightly lighter than those of common concrete. Regarding the mix proportion of cement pastes, changes in unit weight were observed based on a fixed aggregate size. The unit weight increased with the amount of binders but decreased with the increase of w/c ratios as shown in Figures
Unit weight of specimens comprising various particle sizes.
Unit weights for particle A
Unit weights for particle B
Unit weights for particle C
Unit weights for particle D
Table
The water permeability coefficients for various mix proportions.
Label |
|
Label |
|
Label |
|
Label |
|
---|---|---|---|---|---|---|---|
25A50C | 0.1140 | 35A50C | 0.0997 | 45A50C | 0.0881 | 35B80A | 0.0430 |
25A60C | 0.1052 | 35A60C | 0.0555 | 45A60C | 0.0464 | 40B80A | 0.0446 |
25A70C | 0.0852 | 35A70C | 0.0323 | 45A70C | NA | 45B80A | 0.0421 |
25A80C | 0.0436 | 35A80C | 0.0304 | 45A80C | NA | 35B80S1 | 0.0454 |
25B50C | 0.1259 | 35B50C | 0.1192 | 45B50C | 0.1176 | 35B80S2 | 0.0441 |
25B60C | 0.1163 | 35B60C | 0.1044 | 45B60C | 0.0925 | 35B80S3 | 0.0444 |
25B70C | 0.0864 | 35B70C | 0.0585 | 45B70C | NA | ||
25B80C | 0.0857 | 35B80C | 0.0439 | 45B80C | NA | ||
25C50C | 0.1423 | 35C50C | 0.1273 | 45C50C | 0.1210 | ||
25C60C | 0.1283 | 35C60C | 0.1199 | 45C60C | 0.1097 | ||
25C70C | 0.1185 | 35C70C | 0.1118 | 45C70C | NA | ||
25C80C | 0.1126 | 35C80C | 0.1046 | 45C80C | NA | ||
25D50C | 0.1440 | 35D50C | 0.1355 | 45D50C | 0.1331 | ||
25D60C | 0.1350 | 35D60C | 0.1292 | 45D60C | 0.1283 | ||
25D70C | 0.1284 | 35D70C | 0.1131 | 45D70C | NA | ||
25D80C | 0.1149 | 35D80C | 0.1105 | 45D80C | NA |
The mix proportion of particle D exhibited an optimal water permeability coefficient
Water permeability coefficients of specimens comprising different aggregate sizes: (a) aggregate A; (b) aggregate B; (c) aggregate C; (d) aggregate D.
For the different aggregate sizes, the water permeability coefficients decreased as binder w/c ratios increased. This is because at low w/c ratio, binders are highly viscous, enabling the binder to fully cover the aggregates. Intact and fully covered aggregate forms after specimens solidified, and point-to-point contact among the aggregates remains, yielding a void structure that forms a path for water permeation. By contrast, with high w/c ratios, because binders have great fluidity, excess binders that cannot cover aggregates may block the path, thereby decreasing water permeability.
In addition, as the aggregate size increased, the water permeability of pervious concrete increased. For the conventional concrete, three phases (mortar, interface transition zone, and coarse aggregates) exist. The interface transition zone (ITZ) has the worst property among these three phases. It means that the mechanical strength of ITZ is weakest and the water permeability of ITZ is highest since the microstructure of ITZ contains more microcracks, voids, and so on. Therefore, it is well known that the ITZ dominates the behaviors of conventional concrete. If the volume fraction of ITZ increases, a lower compressive strength and a higher permeability coefficient then are expected. Consequently, as the aggregate size was smaller, the volume fraction of ITZ was expected to be larger. It then becomes very puzzling why the water permeability coefficient increased as the aggregate size increased. The reason is explained as the following. For the pervious concrete, four phases (paste, ITZ, coarse aggregates, and designed porosity) exist. Unlike the conventional concrete which adopts mortar to fill the space between aggregates, we only partially fill the space between aggregates by binder for pervious concrete. This concept intentionally makes some porosity inside concrete in order to allow water penetration. Among these four phases, the designed porosity has the worst properties. It has no mechanical strength at all and highest water permeation coefficient. Therefore, the volume fraction of the porosity dominates the behaviors of pervious concrete. When aggregate size is smaller, the initial porosity after packing is smaller. Consequently, when the volume percent of filled voids is the same, the remaining porosity for pervious concrete made with smaller size aggregates is smaller. Therefore, the water permeability coefficient becomes lower.
The internal structure of pervious concrete is relatively less compact because using an insufficient amount of binders produces voids. Water permeability is primarily affected by connected porosity, which can be measured through experimental tests. As shown in Figures
Connected porosity of specimens comprising different aggregate sizes: (a) aggregate A; (b) aggregate B; (c) aggregate C; (d) aggregate D.
Table
The results of the compressive strength test.
Label | Compressive strength (MPa) | Labe1 | Compressive strength (MPa) | Label | Compressive strength (MPa) | Label | Compressive strength (MPa) |
---|---|---|---|---|---|---|---|
25A50C | 17.49 | 35A50C | 12.30 | 45A50C | 10.62 | 35B80A | 28.73 |
25A60C | 19.01 | 35A60C | 16.01 | 45A60C | 14.83 | 40B80A | 24.98 |
25A70C | 22.61 | 35A70C | 20.95 | 45A70C | — | 45B80A | 17.49 |
25A80C | 25.67 | 35A80C | 24.94 | 45A80C | — | 35B80S1 | 21.98 |
25B50C | 17.07 | 35B50C | 11.87 | 45B50C | 8.74 | 35B80S2 | 15.43 |
25B60C | 17.45 | 35B60C | 14.49 | 45B60C | 11.62 | 35B80S3 | 7.68 |
25B70C | 20.36 | 35B70C | 18.81 | 45B70C | — | ||
25B80C | 21.95 | 35B80C | 20.86 | 45B80C | — | ||
25C50C | 16.26 | 35C50C | 11.24 | 45C50C | 7.49 | ||
25C60C | 16.86 | 35C60C | 13.18 | 45C60C | 9.49 | ||
25C70C | 20.01 | 35C70C | 15.51 | 45C70C | — | ||
25C80C | 21.38 | 35C80C | 16.49 | 45C80C | — | ||
25D50C | 13.45 | 35D50C | 10.34 | 45D50C | 5.62 | ||
25D60C | 13.68 | 35D60C | 11.87 | 45D60C | 7.93 | ||
25D70C | 17.32 | 35D70C | 14.86 | 45D70C | — | ||
25D80C | 19.20 | 35D80C | 15.61 | 45D80C | — |
Compressive strengths of specimens comprising different aggregate sizes: (a) aggregate A; (b) aggregate B; (c) aggregate C; (d) aggregate D.
It can be found that the compressive strength decreased as the aggregate size increased. Similar results were also found for other mechanical properties such as splitting tensile strength test and flexural strength test. As explained above, for the conventional concrete, the property of ITZ dominates the property of concrete since ITZ plays as the weakest part in concrete. However, for pervious concrete the weakest part now is designed void. As an increase in aggregate size, a higher volume of void then is expected under the same condition. In such a manner, the compressive strength decreased. Similar result has been observed in [
Figures
Splitting tensile strengths of specimens comprising different aggregate sizes: (a) aggregate A; (b) aggregate B; (c) aggregate C; (d) aggregate D.
Furthermore, the splitting tensile strength decreased as the aggregate size increased. The reason has been given in Section
Figures
Flexural strengths of specimens comprising different particle sizes: (a) aggregate A; (b) aggregate B; (c) aggregate C; (d) aggregate D.
Soundness tests can simulate the resistance of pervious concrete specimens to sulfate attacks. In this study, 12-day old specimens were immersed in an oversaturated magnesium sulfate solution and then washed before subjecting to a round robin test. Subsequently, the weight loss percentages of the specimens were measured to infer the resistance to sulfate attacks; the results are shown in Figures
The weight loss percentages of specimens comprising different aggregate sizes that were immersed in a sulfate solution: (a) aggregate A; (b) aggregate B; (c) aggregate C; (d) aggregate D.
For all the aggregate sizes, maximum weight loss occurred with 50% binder-filled void, and weight loss increased as the amount of binder used increased. Regarding binder characteristics, weight loss was minimal at a w/c ratio of 0.25 and increased with increasing w/c ratio. This was caused by the overall compactness of the specimen. When a small amount of binder was used, increased number of voids in the specimen became available for sulfate attacks and reactions between cements and aggregates. As with w/c ratios, after high-w/c binders solidified, the amount of small voids that remained after water loss or hydration was greater than that of low-w/c binders. This increase in void amount created paths for sulfate attacks, thus decreasing the sulfate-attack resistance of high-w/c pervious concrete containing low amount of binders.
The specimens comprising four various aggregate sizes were subjected to permeability and connected porosity tests. The test results were then used to plot an
The relationship between porosity and water permeability coefficient.
To determine the correlation between compressive strength and water permeability, these two variables were measured for each particle size and then an
Correlation between compressive strength and water permeability coefficient.
Water permeability coefficient and connected porosity decreased with the increase of binder amounts but increased with increasing aggregate size. Pervious concrete with binders of low w/c ratio is highly viscous, which facilitated covering the aggregates. This enabled sufficient binding between particles and effectively reduced excess binders from blocking water permeation paths, thereby influencing water permeability. Under identical connected porosity, the specimens with small particles had small sectional areas in the connected voids, producing meandering paths for water permeation. Specimens consisting of large particles had large sectional areas and straight paths. Thus, the velocity of the water infiltrated in the specimen differed, yielding variation in the flow volume of the water flowing out of the specimen. Mechanical strength decreased with increasing water permeability. Although using substantial amount of binders can enhance mechanical strength, permeability might decrease because the volume percent of binder-filled voids increases. The amount of binder used was directly proportional to mechanical strength, and increased aggregate size decreased mechanical strength. Alkali-activated slag paste with L/Sg = 0.35 and 0.4 had greater mechanical strength than the cement-paste control did. Consequently, using appropriate amount of alkali-activated slag as a binder can effectively enhance the mechanical strength of pervious concrete. The mechanical strengths of the specimens with binders containing 10% silica fume were superior to those of the control specimen. This result was not observed for specimens with binders containing 20% or 30% silica fume, possibly because excessive amount of silica fume was added. Therefore, adding a suitable amount of silica fume to binders can enhance the overall mechanical strength of pervious concrete. The weight-loss percentage of pervious concrete experiencing sulfate attacks increased as the w/c ratio of cement pastes increased. Weight loss percentage was directly proportional to aggregate size, because the stacking of large aggregates generated large voids, which created paths for sulfate to infiltrate specimens and induce reactions. Specimens composed of alkali-activated slag binder exhibited a superior resistance to sulfate attacks than those consisting of cement pastes did.
The authors declare that there is no conflict of interests regarding the publication of this paper.