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Experimental study on the effects of water content to cement soil

Yongqin Wen 1, a , Xiangdong Shen 2,b , Chao Cui 3,c , Yaping Cui 4,d 1Jilin Jianzhu University, Changchun 130118,China

2 Inner Mongolia Agricultural University,Hohhot 010018,China3Yu Xing Supervision Company,Changchun 130118,China

4 Jilin Jianzhu University,Changchun 130118,Chinaaemail: wyqwen@126.com, bemail: NDSXD@163.com,cemail: cchcui@126.com demail: 783780427@qq.Com

Keywords: Natural pumice powder; Cement composite soil; Strength; Triaxial test; Stress – strain;Water content

Abstract: With pumice as the additive agent used in cement composite soil.In order to test thestrength of the composite cement soil,the triaxial shear test were tested in the lab with differentwater content (10%,15%,20%,25%), different curing periods(7d,28d,60d),The results show that thestrength of the composite cement soil first added,and then reduces. there is an optimum amount15%.The pumice powder may evidently improve the mechanical properties of soft soil which hasthe characteristic of rich-water content.

1.The introduction

Soft foundations are frequently encountered in road engineering, coastal engineering andvarious infrastructure projects. Its bearing capacity generally cannot meet the requirements ofengineering construction because of its low strength and high compressibility [1] , need to adoptcertain modified reinforcement measures. In order to meet the requirements of foundation strength,the soil-cement pile and cement solidified soil is widely used as the commonly used material, sincethe 1970 s, researchers have carried out a lot of research at home and abroad [2-10] . Xu Chao [3] , YeGuanbao,Gao Guorui [11] [12] studied macroscopic and microscopic characteristics of cement-soil andanalyzed the cement solidification of soft soil; Ning Baokuan [13] , Chen Sili [14] and others adopt themethod of experiment to study the soil in a variety of environmental factors (water and differentconcentrations and different pH, different chemical solutions, etc.) under the influence ofmechanical properties; Hao Jutao [15] from the angle of mechanics of materials of mechanical

properties of soil are discussed. The goal of the research is to make full use of local naturalresources and improve the strength of soft ground, this paper with pumice as the additive agentused in cement composite soil, modification effect of pumice are studied by cement-soilexperiment.

2. The test raw material and the method

2.1 Test materialsThe clay of test taken from Hohhot, a site for the newly piled all disturbed clay, loose soil, soil

and its main physical property indexes are shown in table 1.

Tab.1 Main performance of soilliquid

limit[%] plastic

limit [%] plasticityindex

maximum drydensity [g/cm 3]

the optimal moisturecontent [%]

33.5 21.5 12 9.99 2.05

Cement produced by Ordos city of Inner Mongolia P.O 42.5 R ordinary Portland cement, natural pumice produced by xilingol league area of Inner Mongolia,natural pumice through the 0.5 [mm]

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soil sieve after grinding , the chemical composition of these two kinds of material are shown intable 2.

Tab.2 Main chemical composition(by mass)of P.O.42.5 portl cement and pumice powder [%]material SiO2 Al 2O3 CaO MgO SO 3 Fe 2O3 K 2O TiO 2 Na 2O

cement 22.06 5.13 64.37 1.06 2.03 5.25 0 0 0 pumice powder 48.88 12.90 8.70 6.10 0.15 14.00 1.58 2.20 2.98

The content of SiO2 in Natural pumice is 48.88%, content is larger, the rate of silicon andaluminum content that in pumice is higher, and its structure mostly amorphous vitreous, thereforehas a certain activity, and this kind of activity can improve the performance of cement compositesoil interface.

Pumice is porous lightweight volcanic material, has developed pore structure, among porositymostly full of the amorphous vitreous, mostly brown or black iron, exterior morphology andmicroscopic structure as shown in figure 1, near the crater high-temperature baking tests orweathering is reddish brown, the main mineral composition including [16] : sodium silicate, feldspar,quartz, biotite and hornblende.

Fig1. Original morphology picture and SEM picture of the pumice

The maximum dry density and optimum water content of cement-soil were tested in the labwith different cement content by compaction test,the results are shown in table 3.

Tab.3 Maximum dry density and optimum moisture content

cement content [%] 8 12 16 20

maximum dry density [g/cm 3] 2.16 2.14 2.11 2.09

optimum water content [%] 8.55 8.13 8.35 8.742.2 Test methodThe test instruments is made in Nanjing soil instrument factory,the type of / TSZ - 6A / strain

controlled triaxial apparatus, maximum load testing process is 60 [KN],in accordance with thestandard of soil test method (GB/T50123-2002) of the provisions, the strain rate of 3% per minute,the sample size for φ39.1mm×h80mm, test schemes are shown in table 4.

Tab.4 Test plan of pumice cement soil

number cementcontent[%]

pumice powdercontent [%]

original soil watercontent [%]

1

16 8

52 103 154 20

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3. The test results and analysis

3.1 The relationship between unconfined compressive strength and water content of cement soil

The no consolidated undrained triaxial shear test was done for the sample of pumice cementcomposite soil, the results are shown in figure 2:

Relationship between strength and water content of soil

0

0.51

1.52

2.53

3.54

4.55

0% 10% 20% 30%

water content of soil

t h e u n c o n f i n e d c o m p r e s s i v e s t r e n g

/ M P a 7d

28d

60d

Fig2. Relationship between compressive strength and water content of composite cement soil

The results of figure 2 show that the strength of cement composite soil which cement content is16% , pumice content is 8%, with the increase of water content the strength first increases thendecreases, water content increased from 5% to 15%, the strength increased and reached the peakstrength.After that with the increasing of water content the strength is reduced.The unconfined

compressive strength of the composite cement soil increases with the increase of the curing age, the peak intensity of each curing age appears under the water content 15% . the test results show thatwhen the cement content of 16% , the best content of water is 15%.

3.2 The stress-strain relationship under different water contentThe relationship between stress and strain of pumice cement soil were analyzed, the resultsexpressed in the figure 3.

Confining pressure400KPa

ε

σ

σ

5%water content

10%water content

20%water content

15%water content

Confining pressure 800KPa

ε

σ 1

- σ 3

/ M P a

5% water content

10%water content

20%water content

15%water content

Fig3. Stress-stain curves of composite cement soil with different water content

The curves of the figure 3 show that: At the same axial strain facies ,the maximum principal stressdifference, when water content was 15%, principal stress reached the peak strength,with theconfining pressure of 400[KPa] as an example, water content from 5% to 20%, the Stress-staincurves are singnificantly changed, the triaxial compression condition is advantageous to the pumice

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cement-soil strength increase, increases with the increase of confining pressure difference of principal stress, the linear change period lengthen, its change is very similar the stress-strain curveof rock. using damage theory of rock to explain the damage process .When the load is small, almostno damage occur, pumice cement-soil similar pure elastic material, and stress-stain curvesapproximation in a line. Internal micro cracks appear when the load continues to increase,effective

bearing area of the specimens decrease the performance of the macro elastic modulus decreases,and the specimens deformation speed of stress-strain curve is convex type, when the load is close to

breaking load, damage micro cracks larger interconnected specimen internal macro cracks appear,with the continue development of fracture specimens bearing capacity continues to fall finallycracks due to friction and confining pressure effect, the basic remain unchanged despite the strainincreasing stress, residual strength.

In the process of the experiment, when the confining pressure is small, soil caused by a lack oflateral restraint, has obvious lateral deformation, specimen damage close to the brittle failure, whenthe confining pressure increases, the specimens under the action of load has obvious compressiondeformation of ballooning,with obvious plastic deformation characteristics. Specimens compressiondeformation is as shown in figure 4.

Fig4.The picture of Specimens compression deformation

4. Conclusion

With pumice as the additive agent used in cement composite soil. In order to study the effect of pumice powder, the unconfined compression resistance were tested in the lab,the conclusion shownthat:

(1) With the increase of water dosage the strength first increases then decreases, the relationship between strength and water content of cement soil were analyzed, based on the analysis,they accordwith cubic polynomial relationship.

(2) With pumice as the additive agent used in cement composite soil the mechanical properties ofsoil improved,adding pumice can make the reinforcement of soft soil water content increased from8.5% to 15%, greatly enhance the high water content of the soil reinforcement of soft soilsuitability.

(3) With the increase of confining pressure, the principal stress difference increasing, confining pressure is small,specimen damage close to brittleness, increases as the confining pressure,materialgradually close to the ideal elastic-plastic material, the specimen presented ballooning, showingobvious plastic deformation characteristics.

Acknowledgements

This work was financially supported by the National Natural Science Foundation (51069008),theInner Mongolia Autonomous Region Natural Science Foundation (2009 ms0705),the InnerMongolia Autonomous Region Project of Institutions of Higher Learning Scientific Research(NJ09046) ,the Dr Scientific Research Fund Project of Jilin Jianzhu University and Ministry ofHousing and Scientific research project of Urban-Rural Development(2013-K1-54).

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