The uniaxial compression response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined. Pore structure parameters such as porosity, threshold diameter, mean diameter, and total amounts of macropores, as well as shape and size of micropores are quantified by using mercury intrusion porosimetry (MIP) technique. Test results indicate that strains at peak stress and compressive strength decreased with the increasing sand-cement ratio due to insufficient binders to wrap up entire sand. A compression stress-strain model of normal concrete extending to predict the stress-strain relationships of manufactured sand mortar is verified and agreed well with experimental data. Furthermore, the stress-strain model constant is found to be influenced by threshold diameter, mean diameter, shape, and size of micropores. A mathematical model relating stress-strain model constants to the relevant pore structure parameters of manufactured sand mortar is developed.
Natural sand has risen in price and the excessive exploration appears in some area, which will lead to the destruction of the environment and the nature energy crisis. However, manufactured sand produced by rock can meet the strategic requirement of sustainable development and save natural resource to be an alternative to natural sand. Manufactured sand has good characteristics of stable quality, adjustable particle gradation, rough surface, and sharp particle guarantee excellent mechanism of materials prepared by it [
At present, experimental researches on cement-based materials prepared by manufactured sand are restricted to macro mechanical properties [
The objective of this research is to develop simplified mathematical models for the interpretation of MIP data and to extract relevant pore structure parameters which can be used for prediction of uniaxial compressive response. Uniaxial compressive response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined so as to bring out the influence of different pore structure features on it. Pore structure features are quantified by using mercury intrusion porosimetry technique. Uniaxial compressive stress-strain relationships are obtained for manufactured sand mortars and are related to pore structure parameters. It is believed that a proper understanding of the influence of pore structure features on compressive stress-strain relationship can lead to optimized material design for the desired properties of manufactured sand mortar.
Ordinary Portland cement without mineral additions and manufactured sand consisting mainly of calcium carbonate were used as binder and fine aggregate, respectively. The density of cement is 3200 kg/m3, and that of manufactured sand is 2650 kg/m3. The gradation test showed that the particle size of the manufactured sand was continuously distributed within 0.075–5 mm without limestone powder. In this experimental research, 12 mix proportions of cement mortar with the water-cement ratio of 0.4, 0.5, 0.6, and 0.7 were prepared, and the sand-cement ratios were adjusted according to fluidity of the mixtures, as shown in Table
The mix proportion of 12 manufactured sand mortars.
Specimens |
|
|
Fluidity (mm) |
---|---|---|---|
M1 | 0.4 | 1.0 | 257.5 |
M2 | 0.4 | 1.5 | 215.0 |
M3 | 0.4 | 2.0 | 162.5 |
M4 | 0.5 | 2.0 | 257.5 |
M5 | 0.5 | 2.5 | 187.5 |
M6 | 0.5 | 3.0 | 150.0 |
M7 | 0.6 | 2.5 | 265.0 |
M8 | 0.6 | 3.0 | 237.5 |
M9 | 0.6 | 3.5 | 150.0 |
M10 | 0.7 | 3.0 | 267.5 |
M11 | 0.7 | 3.5 | 242.5 |
M12 | 0.7 | 4.0 | 177.5 |
The compressive response of manufactured sand mortars were determined using a 1000 kN closed-loop universal machine operating in uniform loading controlled mode of 1 kN/s according to ASTM C349 [
A specimen placed on test setup.
The total porosity of the mortar samples was estimated from the weight of the test sample after drying in an oven at 105°C until reaching constant weight, followed by saturation of the sample by immersion in water for 72 hours, according to the ASTM C642-97 [
Mercury intrusion porosimetry (MIP) is a widely used method for measuring the pore size distribution of cement-based materials. In MIP test, samples are intruded into a chamber; the chamber is evacuated; the samples are surrounded by mercury and pressure ranging from subambient to 60,000 psi (414 MPa). The contact angle and surface tension of mercury were assumed to be 117° and 0.484 N/m, respectively. On the pressure, the smallest pore size into which mercury can be intruded is 2 nm, and the largest pore size which can be intruded is 200 mm with subambient pressure. The MIP results were obtained in the form of raw data representing cumulative intruded volume versus pore diameter curves and logarithmic differential intruded volume versus pore diameter of cement mortar curves.
Pore size distribution as well as some simplified parameters will be developed using MIP technique. Some pore structure parameters from MIP curves for the strength of cement composites seem to be useful from some experimental researches [
Typical MIP curve divided into three regions.
Taeun’s research [
As mentioned by Carniglia [
Pore structure parameters shown in a typical MIP cumulative curve.
In this section, the pore size distributions of manufactured sand mortars with different mix proportions after curing 28 days were discussed. The cumulative intrusion volume versus logarithm pore diameter curves is shown in Figure
Cumulative intrusion volume versus pore diameter curves for all mix proportions of manufactured sand mortars.
Typical uniaxial compressive stress-strain curves for all different mix proportions of manufactured sand mortars.
The MIP data indicated a threshold diameter below which there is a relatively little intrusion and immediately above which rapid intrusion commences. This corresponds to the threshold region, namely, Region II of inflection, following an almost horizontal portion of cumulative intrusion curves as shown in Figure
Pore structure parameters for each composition are summarized in Table
Pore structure parameters for all mix proportions of manufactured sand mortars.
Specimens |
|
|
|
|
|
|
---|---|---|---|---|---|---|
M1 | 0.2213 | 0.018 | 0.065 | 0.055 | 0.017 | 0.464 |
M2 | 0.2003 | 0.027 | 0.067 | 0.062 | 0.019 | 0.382 |
M3 | 0.1845 | 0.042 | 0.065 | 0.066 | 0.025 | 0.311 |
M4 | 0.2213 | 0.023 | 0.076 | 0.062 | 0.017 | 0.419 |
M5 | 0.2119 | 0.036 | 0.078 | 0.071 | 0.02 | 0.357 |
M6 | 0.1892 | 0.03 | 0.079 | 0.075 | 0.018 | 0.388 |
M7 | 0.2241 | 0.014 | 0.085 | 0.071 | 0.018 | 0.378 |
M8 | 0.2049 | 0.027 | 0.088 | 0.075 | 0.02 | 0.344 |
M9 | 0.2116 | 0.084 | 0.093 | 0.109 | 0.027 | 0.252 |
M10 | 0.2365 | 0.039 | 0.095 | 0.095 | 0.016 | 0.37 |
M11 | 0.221 | 0.062 | 0.096 | 0.121 | 0.018 | 0.316 |
M12 | 0.2145 | 0.026 | 0.097 | 0.116 | 0.021 | 0.296 |
The typical uniaxial compressive stress-strain curves for all mix proportions of manufactured sand mortars are shown in Figures
In the past, many studies [
Typical stress-strain relationship fitting results of manufactured sand mortar.
In this section, analytical model characterized stress-strain curve model parameter
Intercorrelation matrix of model terms for compressive response.
Model terms |
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|
|
1 | 0.19 | 0.63 | 0.75 | 0.70 | 0.56 | −0.81 |
|
1 | −0.04 | 0.48 | 0.28 | −0.51 | −0.21 | |
|
1 | 0.42 | 0.64 | 0.62 | −0.74 | ||
|
1 | 0.88 | 0.02 | −0.57 | |||
|
1 | 0.25 | −0.74 | ||||
|
1 | 0.78 | |||||
|
1 |
List of model selection criteria,
Case |
|
|
|
|
|
|
|
AIC |
---|---|---|---|---|---|---|---|---|
1 | * | 0.66 | −7.6 | |||||
2 | * | * | 0.78 | −11.1 | ||||
3 | * | * | 0.68 | −6.5 | ||||
4 | * | * | * | 0.84 | −12.7 | |||
5 | * | * | * | 0.79 | −9.2 | |||
6 | * | * | * | 0.87 | −15.1 | |||
7 | * | * | * | 0.81 | −10.6 | |||
8 | * | * | * | * | 0.88 | −13.9 | ||
9 | * | * | * | * | 0.87 | −12.8 | ||
10 | * | * | * | * | 0.89 | −15.6 |
Intercorrelation matrix of modified model terms for compressive response.
Model terms |
|
|
|
|
---|---|---|---|---|
|
1 | −0.82 | 0.52 | 0.75 |
|
1 | −0.45 | −0.56 | |
|
1 | 0.89 | ||
|
1 |
A multiple nonlinear regression model was found to provide a higher degree of predictive accuracy by Deo and Neithalath [
Coefficients for multiple linear model and multiple nonlinear model.
Model terms |
|
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|---|
Coefficient | −1.7 | 5.1 | 1.9 | 27.2 | −9.0 | 54.3 | −1.6 | 0.92 |
|
||||||||
Model terms |
|
|
|
|
|
|
AIC | |
|
||||||||
Coefficient | −2.01 | −0.04 | 32.11 | −6.80 | 67.03 | 0.89 | −15.62 | |
|
||||||||
Model terms |
|
|
|
|
|
AIC | ||
|
||||||||
Coefficient | −0.17 | −1.14 | −1.29 | 28.96 | 0.91 | −16.10 |
Experimental data and model fits for the stress-strain relationship by pore structure parameters of MS mortar.
The primary objective of this paper is to develop a simplified mathematical model relating compressive stress-strain relationship to its relevant pore structure parameters other than total porosity derived by MIP technique. Experiments and statistical analysis were carried out and the following fundamental conclusions can be drawn: threshold diameter increases with increasing sand-cement ratio and water-cement ratio. The threshold region (Region II) becomes flattened and horizontal along with increasing sand concentration in manufactured sand mortar; this is mainly because of the reorientation effect of fine aggregates on pore structure; strains at peak stresses and compressive strength of manufactured sand mortar decrease with increasing water-cement ratio and sand-cement ratio in all specimens except for that, with 0.4 w/c, the relatively lower compressive strength values can be attributed to higher w/c and sand-cement ratio in these mixtures, in which there is no sufficient inclusion binder of manufactured sand; a model proposed for the stress-strain relationship of normal concrete was found in accordance with experimental data of manufactured sand mortar with a higher precision. The model constant was related to pore structure parameters, while threshold diameter, mean diameter, size, and shape of micropores are responsible for it other than porosity and total amounts of macropores. A mathematical model was developed relating compressive response to relevant pore structure parameters of manufactured sand mortar.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors are grateful to the National Natural Science Foundation of China for the financial support (no. 51279054).