Abstract

1 Introduction

With the highly development of highway in China, the semi-rigid base asphalt pavement has been considered as a promising candidate in high-level asphalt pavement for its high bearing capacity and low cost ¹1 Yang H, Tang X, Hao P, Dai J. Evaluation method for anti-cracking performance of semi-rigid base course. Journal of Chang’an University (Natural Science edition) . 2002;22(4):13-15.

2 Zhang H, Lu S, Le F. The theory of framework dense pavement and its supporting construction technology. Beijing: China Communications; 2010. p.211-248.

3 Jing Z, Liu J. Experimental research on dynamic deformations of semi-rigid structures of subgrade bed-mudstone of red beds, Rock and Soil Mechanics, 2010;31(7): 2116-2121.^-44 Tian L, Feng D. Study on evaporation shrinkage of cement stabilized graded stone with framework and dense structure. Low temperature Architecture Technology . 2010;32(7):1-5. . However, the crack formation limits the development of semi-rigid based materials, and finally increases the risk of deterioration of the correspondingly mixes ⁵5 Coree BJ, Hislop WP. A laboratory investigation into the effects of aggregate-related factors on critical VMA in asphalt paving mixtures. Asphalt Paving Technology: Journal of the Association of Asphalt Paving Technologists. 2001;70:70-131.

6 Li Z, Liu T. Study on moisture performance of cement stabilized gravel under hydrodynamic pressure. Journal of Harbin Institute of Technology (New Series). 2012;19(2): 47-52.

7 Reza SA, Dallas NL, Eyad M. Evaluation of the impact of fines on the performance of lightly cement-stabilized aggregate system. Transportation Research Record: Journal of the Transportation Research Board. 2008;2026:81-88.^-88 Taha R, Al-Harthy A, Al-Shamsi K, Al-Zubeidi M. Cement stabilization of reclaimed asphalt pavement aggregate for road bases and subbases, Journal Material Civil Engineering. 2002;14(3): 239-245..

In the latest decade, the researchers found that the thorough method to prevent the formation of crack reflection is to decrease the cement content and apply the low dosage cement stabilized graded stone. Yu ⁹9 Yu X, Huang X. Analysis on shrinkage and temperature contraction character for low dosage cement stabilized aggregate. Journal of Highway and Transportation Research and Development. 2007;24(7):52-55. found that when the cement content is under 3%, the shrinkage coefficient of 28 days is sensitive to cement content. Temperature contraction coefficient of both 7 and 28 days raise with the increasing of cement content and temperature contraction coefficient of 7 and 28 days in high temperature is remarkably bigger than that in common and low temperature. Zeng ¹⁰10 Zeng M, Luo D, Wu C, et al. Anti-cracking properties of cement stabilized crushed stone pavement base materials of different aggregate structure, Journal of Human University (Natural Science). 2013;40(10): 1-7. got that both the non-cracking ultimate temperature drops and the moisture losses decreases with the increase of cement content. The ultimate temperature drops and the moisture losses of frameworking materials are 19.9%~24.3% and 3.6%~6.8% high than those of floating materials, respectively. Motohiro and Masaru¹¹11 Motohiro N, Masaru Y. Application of crushed cement-stabilized construction sludges to base course. Mem Fac Eng., Osaka City Univ. 2003;44:83-87. http://dlisv03.media.osaka-cu.ac.jp/infolib/user_contents/kiyo/DB00011055.pdf
http://dlisv03.media.osaka-cu.ac.jp/info... produced the crushed cement-stabilized constrtion sludges (CCSS) and the correspondingly CBR of 8% CCSS changed remarkably by moisture contents. Disfani ¹²12 Disfani MM, Arulrajah A, Haghighi H, Mohammadinia A, Horpibulsuk S. Flexural beam fatigue strength evaluation of crushed brick as a supplementary material in cement stabilized recycled concrete aggregates. Construction and Building Materials. 2014;68:667-676. researched the flexural beam fatigue strength evaluation of crushed brick in cement stabilized recycled concrete aggregates. The cement-stabilized blends with crushed brick as a supplementary material with up to 50% brick content and 3% cement were found to have physical and strength properties, which would comply with road authority requirements.

In this paper, the mechanical, dry shrinkage and frost resistance performance of cement stabilized graded stones with cement content of 3%, 4%, 5%, 6% and 7% were investigated. Furthermore, Mercury intrusion porosimetry (MIP) and SEM analysis provided a nano-scale analysis for the influence of moisture content in cement stabilized graded stones.

2 Experimental Procedures

2.1 Materials

Ordinary Portland 32.5R cement was used in this study, which produced from Shandong Shanshui Cement Co., Ltd., China; its physical properties are shown inTab.1. Coarse aggregate was limestone gravel, which provided by Nanjing Quanshui Quarry. The correspondingly gradation was shown in Tab.2.

2.2 Preparation and testing

According to the Chinese Standard JTG E51-2009, the optimum moisture content and maximum dry density were confirmed by the method of compaction test of cement stabilized graded stones. Then the samples were prepared with 98% compaction degree, the resulted optimum moisture content and maximum dry density. 7 days unconfined compressive strength (JTG E51 T0805-1994), 90 days indirect tensile strength (JTG E51 T0806-1994) and 90 days elastic modulus (JTG E51 T0852-2009) were all performed on cylindrical specimens with 150 mm height and 150 mm diameter. These tests were all performed on six replicated specimens.

Dry shrinkage tested (ASTM C341 and ASTM C490) were shown on the prism specimen with a certain size of 100×100×400 mm³, which were cured in the standard atmosphere for 7 days. Finally, the specimens were dried and the dry shrinkage were measured till equilibrium conditions existed. The dry shrinkage coefficient was calculated as equation (1).

where ${{\displaystyle \sum }}^{\text{}}\Delta l$ is the accumulated dry shrinkage and L is the initial length of prepared sample.

Frost resistance performance (Chinese Standard GB/T 50082-2009) were performed on 100×100×400 mm³ specimens for 180 days’ curing. The cycle temperature was set as -20~20 °C, and a whole cycle included a 3 hours’ drop temperature and 5 hours’ raise temperature procedure.

After 90 days curing, these prepared samples were soaked in ethanol to stop the hydration reaction, and then put in an oven at 70 °C for about 1 day for drying procedure. Four samples were tested by using an automated mercury porosimeter (AUTOPORE IV 9500 series, Micromertics Instrument Corp., USA), with two low-pressure stations plus one high-pressure station, and with a maximum pressure of 33,000 psia for pore size measurements. Moreover, morphology study was performed with an ultra-high resolution field emission scanning electron microscopy (FE SEM) (NOVA NanoSEM 450, FEI Co. Ltd., USA) at an accelerating voltage of 3 kV with 40~400,000 magnification. Prior to this SEM observation, the prepared samples (1×10×10 mm) were coated an about 20 nm thick Au film layer.

3 Results

3.1 Mechanical performance

The mechanical performance of the mixes with different cement content (3.0%, 4.0%, 5.0%, 6.0% and 7.0%) was shown in Tab.3. With the increasing of cement content, we clearly discerned that the tested mechanical performance was improved, including 7 days unconfined compressive strength, 90 days indirect tensile strength, 90 days elastic modulus and 90 days fracture toughness. With the development of cement hydration, cement could adhesive the aggregates to form a compacted system. The more cement had a better pore parameter system.

3.2 Dry shrinkage test

The gradation of aggregate among the prepared samples were shown in Tab.2 and the added cement content in the mixes was about 3.0%, 4.0%, 5.0%, 6.0% and 7.0%, respectively. The correspondingly dry shrinkage strain and dry shrinkage coefficient were measured and calculated in Tab.4. With the increasing of cement content in mixes, The correspondingly dry shrinkage strain and dry shrinkage coefficient were increased in a certain extent. Especially the cement content exceed 6%, the dry shrinkage strain and dry shrinkage coefficient were significantly deteriorated. Hence, the cement content in a well prepared cement stabilized graded stone was controlled between 4% to 5%.

Furthermore, the moisture content in this cement stabilized graded stone system was researched. The specimens (sample 0, 1, 2, 3) , with different moisture content (4%, 5%, 6%, 7%) in a 6% cement content, were measured and analyzed inTab.5. As is shown in Tab.5, for the prepared samples, with the increasing of moisture content, dry shrinkage strain and dry shrinkage coefficient decreases and reaches the minimum value of about 30.48×10^-6 and 0.14 at the moisture content of 6.0%, and then starts to grow. A sample contained low moisture content has a relatively loose and dry mixtures, which owns a insufficient cement hydration reaction and low strength, finally leads to a weaker dry shrinkage resistance performance. Moreover, the high moisture content sample has a damp and flabby reaction procedure, which has a larger amount of moisture evaporation and further deteriorated dry shrinkage ¹³13 Yang H, Hao P, Dai J. Road performance of cement-stabilized aggregate mixture with expansion agent. Journal of Traffic and Transortation Engineering. 2006;6(1):48-51.

14 Guthrie WS, Brown AV, Eggett DL. Cement stabilization of aggregate base material blended with reclaimed asphalt pavement. Transportation Research Record: Journal of the Transportation Research Board. 2008;2026:47-53.^-1515 Zhu M, Liu W. Shrinkage of cement stabilized macadam base course, Journal of Changsha University of Science and Technology (Natural Science). 2009;6(2): 7-12.. From the perspective of controlling dry shrinkage, the cement stabilized graded stone needs to have a 6.0% moisture content.

3.3 Frost resistance test

After the procedure of freeze-thaw cycle, the cement stabilized graded stone was destroyed by the formed expansion pressure and osmotic pressure in the process of water congeals into ice. The detailed frost resistance performance of prepared cement stabilized graded stone was shown in Fig.1. With the increasing number of freeze-thaw cycles, the frost resistance coefficient was deteriorated, which attributed to the correspondingly pore parameters. In the initial period, the frost resistance coefficient decreased significantly till the eighth freeze-thaw cycle, which reached to a stable condition. After 10 freeze-thaw cycles, the frost resistance coefficient of each mixes was 54%, 64%, 76% and 56%, respectively. The sample with 6.0% moisture content owns the optimum frost resistance coefficient for its appropriate moisture content ¹⁶16 Beata LP. The influence of selected new generation admixtures on the workability, air-voids parameters and frost-resistance of self compacting concrete. Construction and Building Materials. 2012;31:310-319.

17 Wu H, Wei J, Su Q, Ma S. Experimental study on temperature shrinkage and frost resistance of full depeth cold-in-place recycling asphalt pavement materials stabilized by cement and gravel. Forest Engineering. 2012;28(5):76-98.^-1818 Tang C, Shi B, Gao W, Chen F, Cai Y. Strength and mechanical behavior of short polypropylene fiber reinforced and cement stabilized clayey soil. Geotextiles and Geomembranes. 2007;25(3):194-202..

Fig.1
Frost resistance performance of cement stabilized graded stone with different moisture content

3.5 MIP analysis test

MIP was widely applied in concrete science to characterize the pore parameters, e.g., porosity, pore volume and pore size distribution ¹⁹19 Nochaiya T, Chaipanich A. Behavior of multi-walled carbon nanotubes on the porosity and microstructure of cement-based materials. Applied Surface Science. 2011;257(6):1941-1945.^-2020 Chen X, Wu S. Influence of water-to-cement ratio and curing period on pore structure of cement mortar. Construction Building Materials. 2013;38(1):804-812.. Fig.2 shows the variation of dV/dlogD pore volume with pore diameter, and the total pore characterization is summarized in Table 6. Obviously, it can be seen that moisture significantly influence the pore parameters of cement stabilized graded stones. This trend is similar with those of the dry shrinkage and frost resistance performance. The average pore diameter (APD) of sample with 4.0% moisture content is about 66.9 nm, while the APD values of composites are much lower, about 45.7, 28.3 and 36.7 nm, respectively.

Fig.2
MIP analysis of pore parameters of cement stabilized graded stones with different moisture contents

For sample “0”, with the decrease of pore size, dV/dlogD pore volume increases and reaches the maximum value of about 0.253 mL/g at the pore size diameter of 83.8 nm, and then starts to drop. For other mixes, they have the same trends and these maximum values of dV/dlogD pore volume appear in the much finer region of pores, which indicates that the proper moisture content concentrations the pore size. As a kind of porous material, hardened cement stabilized graded stones owns a lower property (mechanical and durability properties) for its weaker pore characterization.

The lower or higher moisture content sample has a damp and flabby reaction procedure for the micro-structure and the pore parameters of prepared composites. The moisture content influences the pore characterization of these composites. Ultimately, the dry shrinkage and frost resistance performance of the composites are enhanced.

3.6 SEM analysis test

It’s believed that the higher dry shrinkage and frost resistance performance of these samples attributes to the correspondingly denser microstructure. FE SEM micrographs of sample “0” and “2” at curing periods of 28 days are shown inFig.3. Compared with the SEM micrograph of sample “0”, the microstructure of sample with 6.0% moisture content is more concentrated and less cracks and pores are seen. In the certain moisture, More C-S-H structure was formed in cement stabilized graded stone with 6.0% moisture content, which improved the correspondingly performance.

Fig.3
SEM analysis of cement stabilized graded stones

4 Conclusion

In this paper, the mechanical, dry shrinkage and frost resistance performance of cement stabilized graded stone were investigated. With 7.0% cement content, the cement stabilized graded stone has the optimum mechanical and the worst dry shrinkage performance. With different moisture content, the dry shrinkage strain and dry shrinkage coefficient were improved with the increasing moisture content, and then obtained the minimum dry shrinkage with 6.0% moisture content, and finally dropped. Compared each frost resistance performance, the same trend was obtained. The optimum frost resistance performance was obtained within 6.0% moisture content.

Furthermore, the MIP analysis of cement stabilized graded stones were obtained and the results showed that the moisture content significantly influence the pore parameters of prepared samples. The sample has a lower porosity and pore diameter with a proper moisture content, i.e. 6.0%. The microstructure of composites shows a nano-scale analysis, which has a concentrated structure with 6.0% moisture content.

Further researches are necessary to obtain better performance of cement stabilized graded stone and more characterizations are needed. However, we believe that our results are helpful for the research of cement stabilized graded stones.

Acknowledgements

The authors would like to express appreciation for the financial support by Open Project Program of National Engineering Laboratory for Technology of Geological Disaster Prevention in Land Transportation.

References

Publication Dates

History