Development of Physical and Engineering Properties of Injected Sand with Latex - Superplasticized Grouts

 

Costas A. Anagnostopoulos

Civil Engineer, Ph.D., Research manager, Laboratory of Soil Mechanics,Geotechnical Engineering Division, Department of Civil Engineering Aristotle University of Thessaloniki, Thessaloniki, Greece
kanagnos@civil.auth.gr

and

Evangelos I. Stavridakis

B.Sc, M.Sc.,Ph.D.,F.G.S., Lecturer Laboratory of Soil Mechanics, Geotechnical Engineering Division, Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki Greece
stavrid@civil.auth.gr

ABSTRACT

Grouting is the most common technical method with many applications, e.g. it is used for soil stabilization and strengthening, for reduction of water ingress to underground facilities or the water loss through a dam foundation etc. Grouts comprise several constituents which are combined in many ways depending on the in situ conditions and the outcome desired each time. Superplasticizers, accelerators, antifreezers, air-entraining agents and many others are generally used to improve the quality of cement grouts and consequently, their effectiveness on strength, durability (especially bond strength), impermeability and resistance to chemical erosion of the grouted soil or rock mass.

A comprehensive research work was carried out concerning the rheological properties of acrylic resin (latex) – superplasticized grouts and their influence, when injected, on the physical (water permeability, porosity) and mechanical characteristics (compressive strength, elastic modulus) of sand.

Keywords: stabilization, cement, acrylic resin, superplasticizer, viscosity, compressive strength, slaking, porosity.

 

INTRODUCTION

Grouting is a special technique developed in recent years, which has found many applications. Grouting is a procedure by which grout is injected into voids, fissures, and cavities in soil or rock formation in order to improve their properties, specifically to reduce permeability, to increase strength and durability or to lessen deformability of the formations. Grouting has a wide application in modern civil engineering world (Nonveiller, 1989). More specifically, it is applied:

Chemical admixtures such as superplasticizers, accelerators, antifreezers, air entraining agents and many others are used to modify the grout properties and protect it from the environmental conditions.

In the last decades powdered emulsions and water-soluble polymers (latex) are widely used as additives in cement grouts due to their potential influence on rheological properties (Allan, 1997), strength (Bureau et al, 2001), durability (internal strength), impermeability (Gao et al, 2002) and resistance to chemical erosion.

The experimental investigation reported herein aims towards the development of a more effective latex modified grouting material for ground improvement. A series of laboratory tests were conducted to investigate the rheological properties of acrylic resin (A.R.) – superplasticized cement grouts with different content of A.R. and the influence of grouting of these modified grouts on the physical (water permeability, porosity) and engineering characteristics (compressive strength, elastic modulus, durability) of sand specimens in relation to the distance from the grouting point.

 

PRINCIPLE OF LATEX MODIFICATION

Latex modification of cement grouts is governed by both cement hydration and polymer film formation processes in their binder phase. The cement hydration process generally precedes the polymer formation process. It is believed that a comatrix phase, which consists of cement gel and polymer film, is formed as a binder according to a three step simplified model shown in Figure 1 (Wagner, 1966).

 



Figure 1. Simplified model of formation of polymer-cement comatrix

First step: When polymer latexes are mixed with fresh cement grout, the polymer particles are uniformly dispersed in the cement paste phase. In such polymer-cement paste, the cement gel is gradually formed by the cement hydration and the water phase is saturated with calcium hydroxide formed during the hydration, whereas the polymer particles deposit partially on the surfaces of the cement gel-unhydrated cement particle mixtures.

Second step: With drainage due to the development of the cement gel structure, the polymer particles are gradually confined in the capillary pores. As the cement hydration proceeds further and the capillary water is reduced, the polymer particles flocculate to form a continuous close-packed layer of polymer particles on the surfaces of the cement gel-unhydrated cement particle mixtures and simultaneously adhere to the mixtures and the silicate layer over the soil particles surfaces. In this case, the larger pores in the mixtures are filled by the adhesive and autohesive polymer particles.

Third step: Ultimately, with water withdrawal by cement hydration, the close-packed polymer particles on the cement hydrates coalesce into continuous films or membranes binding the cement hydrates together to form a monolithic network in which the polymer phase interpenetrates throughout the cement hydrate phase. As a result microcracks are bridged by the polymer films or membranes, which prevent crack propagation and simultaneously a strong cement hydrate-soil particles bond is developed improving the strength characteristics of grouted soil.

 

DESCRIPTION OF THE MATERIALS USED

Sand

Sand used in the testing programme was calcareous – siliceous sand collected from Axios river in Thessaloniki. The mineralogical composition is shown in Table 1.

 

Table 1. Mineralogical composition of the sand used

Mineral Amount (%)
Dolomite 70
Calcium Carbonate 11
Quartz 17
Ilmenite, Magnetite, Haematite 2

 

The grain size distribution is shown in Figure 2. Sand had dry unit weight of gd = 14.85 kN/m3, saturated unit weight of gsat = 19.35 kN/m3 and porosity of 45%.

Cement

Cement used was Microfine Portland cement with specific gravity of Gs = 3.15, specific surface (blaine) of 4,200 cm2/g and characteristic compressive strength of 45 MPa at 28 days. The chemical analysis of cement is given in Table 2.

 

Table 2. Chemical composition of the cement used

Chemical Component SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O Ignition loss
Amount (%) 30 7.5 2 52 2 3 1.5 0.5 1.5

Acrylic Resin (Latex)

Acrylic resin used was an emulsion of a synthetic elastic chemical substance, which increases significantly the bonds within the substrate as additive in cement paste, as well as the cohesion

 



Figure 2. Grain size distribution of the sand

and the engineering strength. It improves also the durability in chemical intrusion, the impermeability and finally the durability in cycles of freezing and thawing. The polymer solids content of the acrylic latex is 35%.

Superplasticizer

Sulphonated melamine formaldehyde condensate (SMF) in the form of an aqueous solution (Water/SMF = 2) was used. Its molecular weight is about 14,000 and the degree of polymerization is n = 55. Its chemical analysis is: C = 23.5%, H = 2.75% and SO4–2 = 37.8%.

 

LABORATORY PROCEDURE

Grouts were prepared with water/cement (W/C) ratio constant at 1. Addition of SMF superplasticizer was 2% by weight of cement. Two modified grouts with A.R./cement ratio of 0.05 and 0.1 were used for experimental work. The A.R./ cement ratio includes the total amount of acrylic emulsion and W/C ratio includes the quantity of water from the emulsion. Grouts were prepared in batches of 10 l and mixed thoroughly for 5 min at least, either for rheological and injection tests.

Rheological properties were measured using a capillary viscometer recording shear stress – shear rate relationship (Figure 3). Capillary viscometer method was chosen instead of the classical cylinder viscometer method, which is commonly used, because it is necessary to determine the flow properties of the grouts under conditions similar to those in situ, and to evaluate the test results in such a way that reliable data are obtained. Another advantage of the capillary viscometer, which was taken into account for this choice, was the limitation of rotating viscometer to pressure of about 100 kPa. The capillary viscometer above is based on the Hagen – Poiseuille’s law. The main objective at this stage of experimental work was to develop a capillary viscometer that can be used to determine the rheological properties of grouts at low and high pressure up to 450 kPa (Maria et al, 2003).

 



Figure 3. Capillary viscometer system

The experimental set up used for the injections was constructed according to A.S.T.M. D 4320 – 93 specifications and comprised the following parts (Figure 4):

The grouted sand specimens were left in the molds for 3 days to develop satisfactory strength and then demolded and cut into lengths of 20nbsp;cm. After that, they were sealed in plastic bags and stored in a 100% relative humidity curing room until the day of testing.

Cylindrical specimens of 10nbsp;cm diameter and 20nbsp;cm height were used for compression tests at 28 days (A.S.T.M. C 109). All tests were performed under a constant strain rate of 0.1%/min (Ata and Vipulanandan, 1999). Specimens of the same size were used for the estimation of porosity according to the referred method of Grimshaw (Grimshaw, pp.421-422, 1971) and water permeability according to A.S.T.M. D 5084 - 00e1 regulation.

Slaking (100 – Id2) was measured using the device and testing procedure developed by Franklin (Franklin and Chandra, 1972).

For the evaluation of the physical and engineering properties of the grouted sand, injection tests on over 50 sand columns were performed.

 

RESULTS AND DISCUSSION

The apparent viscosity – shear rate relationships of unmodified grout and latex superplasticized grouts are presented in Figure 5. The viscosity of all grouts tended to increase when the applied shear rate was raising and revealed that the cement paste behave like a shear thickening material. It is noticed that the lowest and highest viscosity values (unmodified grout, W/C = 1) are 1.6 and 7 times higher than the corresponding one of water (10–3 Pa.s). Grouts admixed with 2% w./c.w. (weight by cement weight). SMF superplasticizer possessed lower viscosity values than those of control grout and especially for shear rate values over 10,000s-1. Addition of 5% w./c.w. A.R. decreased even further the viscosity at the whole range of shear rate values. The average decrease of viscosity was 15% in relation to the obtained values of control grout. Higher dosage of A.R. (10% w./c.w.) had an expected effect on grout viscosity at any shear rate with an average decrease of viscosity 25%. Obviously, the A.R. influences, as a kind of superplasticizer, the grout rheological properties because of the action of the surfactants contained as emulsifiers and stabilizers in polymer latexes.

Figures 6 and 7 show the change in compressive strength and elastic modulus respectively of grouted samples with superplasticized grout and latex-superplasticized grout in relation to the distance from grouting point for 28 days of curing. In the case of grouting with superplasticized

 



Figure 5. Apparent viscosity vs. shear rate
for unmodified grout and (acrylic resin) modified grout with 2% w/cw
superplasticizer and with different dosages of acrylic resin

 



Figure 6. Compressive strength of injected sand specimens
plotted against distance from injection point

 



Figure 7. Elastic modulus of injected sand specimens
plotted against distance from injection point

 



Figure 8. Permeability coefficient of injected sand specimens
plotted against distance from injection point

cement grout (control grout), the compressive strength of the first grouted part was 4,647 kPa with an elastic modulus of 280 MPa whereas for the other parts a rapid decrease of mechanical properties was observed with values fluctuating from 2,330 to 1,750 kPa for strength and 110 to 80 MPa for elastic modulus. Addition of 5% w./c.w. A.R. increased strength and elastic modulus satisfactorily. Especially, elastic modulus exhibited much higher values in relation to those of grouted samples with control grout. The above proves the significant contribution of the formed acrylic resin membranes to an overall improvement in cement-aggregate bond and consequently, in stress-strain response. Infiltration phenomenon, which appeared again, influenced the mechanical properties along the distance from injection point. The enhancement of strength and elastic modulus for the first 20 cm column part was 54% and 143% whereas for the other parts was almost constant with mean value of 32% and 72%, respectively. As the A.R. content was increased to 10% w./c.w. an even higher compressive strength for the first two parts (180% and 412% against the control sample) was obtained, but appeared to be decreased considerably for the other parts having values lower even from those of grouted specimens with control grout (average decrease of 5.5%). Also, similar results were observed in the case of elastic modulus.

This disproportional decrease of mechanical parameters along the distance from injection point substantiates the adverse influence of A.R. at zones with less cement content when added in high dosages. This happens due to the increase of polymer to cement ratio, which leads to discontinuities in the microstructure of grouted sand resultant to the reduction of strength and toughness.

Permeability test results are shown in Figure 8, where permeability coefficient K is plotted as a function of A.R. content and the distance from grouting point. Analysis of the test results indicates that the improvement of permeability depends also on the proportion of the additive and the distance from grouting point. In general, latex modified mortar and concrete show a noticeable decrease in water absorption and water permeability due to the formation of polymer membranes or films from which the larger pores can be filled or sealed. As a result, latex modified mortar and concrete have an improved waterproofness over ordinary mortar and concrete. However, excess of latex could cause discontinuities of the formed monolithic network structure allowing the intrusion of water and hence the increase of water permeability.

Dosage of 5% w./c.w. A.R. had as a result the significant reduction of K for all column parts of grouted samples. The range of K values was 2.4x10-7 – 3.4x10-4 m/s. This improvement on water permeability can be attributed not only to the formation of polymer membranes but also to the fact that the A.R. reduce the viscosity of Portland cement-based grouts and consequently the intake of grout is greater. Addition of 10% w./c.w. A.R. decreased more over the K of the first two parts, 7.2x10-8 and 9.54x10-8 m/s respectively. The other parts exhibited K values slightly higher than the values of control sample, despite of the high grout intake during the injection experiments.

Porosity test results (Figure 9) confirm the above-mentioned observations about the positive influence of A.R. or the adverse influence when existing in high amounts in a poor cement-soil structure. Porosity of 5% A.R. grouted samples was less than that of control samples for all column parts showing the effect of A.R. on a more dense and packed cement-soil structure. Moreover porosity reduction of the first two parts was observed for 10% A.R. grouted samples in contrary with the other parts, which exhibited high porosity values.

Figure 10 shows the change in slaking of grouted specimens with different additive content in relation to the distance from injection point, cured for 28 days. Addition of 5% A.R. reduced strongly the slaking of all parts of grouted material. An “antithesis” between the values of 10% A.R. grouted specimens and the corresponding values of control grout and 5% A.R. grouted specimens is revealed. Particularly, the addition of 10% A.R. did not improve the strengthening

 



Figure 9. Porosity of injected sand specimens
plotted against distance from injection point

 



Figure 10. Slaking of injected sand specimens
plotted against distance from injection point

 



Figure 11. Correlation between slaking and
compressive strength of injected sand specimens

of bonds between cement-soil grains for distance over 40cm from injection point. The above confirms that high dosage of A.R. influences positively the improvement of the grouted system only in a short distance from injection point where high cement content dominates. For longer distance a weakening of cement bonds occurs, because the A.R. polymer films coated the poorly packed grains of cement-sand and prohibit the whole system to be hardened having as a result the increase of porosity and slaking (broken bonds-potential weakening of bonds between grains).

The aforementioned results are depicted clearly in Figure 11 where relationship of negative power curves between slaking and compressive strength are plotted. Control samples reveal lower strength and higher slaking values than 5% A.R grouted samples. In accordance to the above control samples and 5% A.R. grouted samples show lower slaking values than 10% A.R. grouted samples in same strength values. These indications confirm that 10% A.R. influences negatively the development of potential bonds between cement-sand grains and consequently, the enhancement of engineering properties of the grouted material.

 

CONCLUSIONS

  1. Addition of A.R. to cementitious grouts, combined with superplasticizer, modifies their rheological properties resulting in the enhancement of their penetrability and the grout propagation into the soil mass.

  2. Small dosage of A.R. (5% w./c.w.) increases compressive strength and modulus of elasticity and decreases porosity, permeability and slaking of all the parts of grouted soil satisfactorily.

  3. Higher dosage of A.R. improves the properties of grouted soil only to a limited extent evidencing that its efficacy depends directly on the existence of a dense cement-soil structure.

  4. In general, it can be concluded that the use of A.R. as additive in cement grouting purposes contributes significantly to the improvement of grouted soil properties when added in control dosages and in respect to w/c ratio.

 

references

  1. Allan, M.L. (1997), “Rheology of Latex Modified Grouts”, Cement and Concrete Research, Vol. 27, pp 1875-1884.

  2. A.S.T.M. (1993), “Standard Test Method for Laboratory Preparation of Chemically Grouted Soil Specimens for Obtaining Strength Parameters”, West Conshohocken, PA, D4320-93.

  3. A.S.T.M. (2000), “Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter”, West Conshohocken, PA, D5084.

  4. A.S.T.M. (2002), “Standard Test Method for Compressive Strength of Hydraulic Cement Mortars”, West Conshohocken, PA, C109.

  5. Ata, A. and Vipulanandan, C. (1999) “Factors affecting mechanical and creep properties of silicate-grouted sands”, Journal of Geotechnical and Geoenvironmental Engineering, 125, 868-876.

  6. Bureau, L., Alliche, A., Pilvin, P. and Pascal, S. (2001), “Mechanical characterization of a styrene-butadiene modified mortar”, Materials Science and Engineering, A308, pp 233-240.

  7. Franklin, J.A. and Chandra, R. (1972), “The slake durability test”, Int. J. Rock Mech. Min. Sc., Vol. 9, pp 325-341.

  8. Gao, J.M., Qian, C.X., Wang, B. and Morino, K. (2002), “Experimental study on properties of polymer-modified cement mortars with silica fume”, Cement and Concrete Research, Vol. 32, pp 41-45.

  9. Grimshaw, W. Rex (1971), “The Chemistry and Physics of clays and allied ceramic materials”, Ernest Benn Ltd.

  10. Maria, A., Barrufet, Setiadarma, A. (2003), “Experimental viscosities of heavy oil mixtures up to 450K and high pressures using a mercury capillary viscometer”, J. Petroleum Science and Eng., Vol. 40, pp 17-26.

  11. Mollamahmutoglu M. and Littlejohn S. (1997), “Varying temperature and creep of silicate grouted sand”, Ground Improvement, Vol.1, pp 59-64.

  12. Nonveiller, E. (1989), “Grouting. Theory and Practice”,Elsevier, Amsterdam.

  13. Wagner, H.B. (1966), “Compressive Strength of Polymer-Modified Hydraulic Cements”, Industrial and Engineering Chemistry, Product Research and Development”, Vol.5, pp 149-152.

 

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