CEMENT TREATED BASES FOR COST EFFECTIVE RURAL ROADS

Dr. U. C. SahooSchool of infrastructure

IIT Bhubaneswar

National Level workshop on “Pradhan Mantri Gram Sadak Yojana(PMGSY) Revisited “ during 17-18 December, 2019

Introduction

Huge length of road network is being developed inIndia by NRIDA under PMGSY.

For sustainable development of Infrastructure: Need to save the limited natural resources Increase reuse, recycling and reprocessing Need to use the locally available materials Use Eco-friendly Construction Technologies Adoption of New Technologies for developing low cost

durable roads

Stabilization- Need

Costly aggregates-High conveyance cost Soft subgrades Marginal aggregates Sites with drainage issues High Water Table

Materials for Stabilized Layer

Crushed Rock Soils including gravel and sand Lateritic soils/ Gravels Kankar Crushed concrete Brick metal / brick bats Crushed slag Fly ash, pond ash Other industrial wastes

Stabilizers

Lime Cement Lime-fly ash or Lime-slag Other commercial stabilizers

Zydex Nanotechnology (Organosilane chemistry) Terrazyme (A bioenzyme product) RBI Grade 81(Lime based soil stabilizer) Stabil Road Enviortac (Acrylic based Co-polymer) Others..…

Soil-Cement Base

Soil-Cement

Soil-cement is a mixture of locally available soils,Portland cement and water, that hardens aftercompaction and curing to form a strong and durablepavement layer.

This has been used as a pavement base forhighways, roads, streets, parking areas, airports,industrial facilities, and material hauling and storageareas in many developed countries.

For Low volume rural roads, soil-cement can beeffectively used to economise the construction.

Soil-Cement

By stabilizing the soilwith cement, the entiremass is hardened into aslab that results insufficient rigidity andstrength to spread theloads over a large areaof the subgrade.

Unstablized granular base versus soil-cement base (Halsted et al. 2006)

Advantages of Soil-Cement Base

Provides a stronger, stiffer base that reducesdeflections due to traffic loads extending thepavement life.

Thickness requirement for base is less compared togranular bases carrying for the same traffic load asthe loads are distributed over a large area.

A wide variety of in-situ soils can be used,eliminating the need to haul in expensive selectgranular aggregates.

Advantages of Soil-Cement Base

Rutting is reduced due to presence of a stiffercement stabilized base.

Forms a moisture-resistant base that keeps waterout and maintains higher levels of strength.

Provides a durable, long-lasting base in all typesof climates, designed to resist damaged caused bycycles of wetting and drying.

Continues to gain strength with age.

Disadvantages Soil-Cement Base

When soil-cement strengths are too low, it will notprovide adequate support to traffic, resulting inrutting and large deflections.

When the strengths are too high due to excessiveamounts of cement, it may lead to wide shrinkagecracks.

Factors Affecting Cement Stabilization

Type of Soil/ Aggregate Cement Pulverisation and Mixing Compaction Curing Additives

Type of Soil

Almost all types of soil can be stabilized usingPortland cement, because its stability is obtainedfrom the hydration of the cement and not by thecohesion and internal structure of the material (PCA1995).

The most preferred choice of soil-cement base arecoarse-grained soils, because of their ability topulverize and mix more easily than fine-grainedsoils (ACI 230 2009)

Type of Soil

Fine-grained soils require more cement than coarse-grained soils for specified strength of soil-cementbase

Soils having high moisture demands require morecement, making them more prone to dryingshrinkage issues.

According to ACI 230 (2009), coarse-grained soilscontaining between 5% and 35% fines passing theNo. 200 (IS 75 micron) sieve produce the mosteconomical soil-cement base.

Portland Cement

All types of cement have been successfully used forsoil-cement bases.

The required amount of cement varies dependingon the desired properties (strength & durability)and soil type.

Cement contents may range from as low as 4 to ashigh as 16 percent by dry weight of soil (ACI 2302009).

Cement requirements for various soils

(Source: ACI 230, 2009)

Water

Water is necessary in soil cement to help obtainoptimum compaction and for hydration of thePortland cement.

Potable water or other relatively clean water, freefrom harmful amounts of alkalis, acid, or organicmatter may be used.

Higher water content than OMC was observed toadversely affect the strength.

Mix Design

Minimum 7 days unconfined compressive strength of3.0 MPa for base course and 1.7 MPa for sub-basefor application in low volume roads (IRC:SP:72-2015).

The material loss after 12 cycles of wetting anddrying test (carried out as per ASTM D 559) shouldbe determined.

Durability Requirement

(Source: PCA, 1971)

Wet-Dry Durability Test

Wet-Dry Durability Test

Mass Loss after 12 cycles (Granular Lateritic Soil + Cement)

Standards to follow

ASTM-D1632 − 17: Standard Practice for Makingand Curing Soil-Cement Compression and Flexure TestSpecimens in the Laboratory

ASTM- D559- Test Methods for Wetting and DryingCompacted Soil-Cement Mixtures

IRC:SP-89:2010- Guidelines for Soil and GranularMaterial Stabilization using Cement, Lime and Fly Ash

IRC:SP-89-Part:II-2018-Guidelines for the Design ofStabilized Pavements

Construction Procedure

Soil Cement mixing process can be divided into twotypes:Plant-mix stabilizationMix-in-Place stabilization

In-situ stabilization involves the following operations:Preparation of groundSpreading of StabilizerMixing Compaction and Finishing

Construction Process

Stone Grafting

Stone Grafting with 40 mm-25mm size aggregates should bedone before final compaction.

This will ensure good bongingwith the bituminous surfacinglayer.

Curing

Proper curing of soil cement is important becausestrength gain is dependent upon time, temperature,and the presence of water.

About 7-day curing period is desired, during whichtime equipment heavier than rubber-tired rollers isprohibited.

Light local traffic, however, is often allowed on thecompleted soil cement immediately after constructionprovided that the curing coat is not damaged.

Water-sprinkling and bituminous coating are twopopular methods of curing.

Curing

In bituminous curing, the soil cement is commonlysealed with bitumen emulsion.

Before emulsion is applied, the surface of the soilcement should be moist and free of dry loosematerials. In most cases, a light application of waterprecedes the bituminous coating.

If traffic is allowed on the soil cement during thecuring period, it is desirable to apply sand over thebituminous coating to minimize tracking of thebituminous material.

Soil Cement Base after Prime Coat

Surfacing over Soil Cement Base

For lighter-duty roads, a two-coat surface dressingis usually recommended as the wearing surfacedirectly on the stabilized base.

The first layer may be constructed with 13.2 mmchips and second coat with 9.5 mm pre-coatedchips.

On heavier-duty roads, an additional 50-100 mmof unbound crushed aggregate is added toincrease section thickness before chip-sealapplication.

Surface Dressing

Finished Road Surface

Photos of Roads Constructed in Balangir, Odisha

Shrinkage and Cracking

Cement-treated soils undergo shrinkage during drying. The shrinkage and subsequent cracking depend on

cement content, soil type, water content, degree ofcompaction, and curing conditions.

Soil-cement made with clays develops higher totalshrinkage, but crack widths are smaller and individualcracks more closely spaced

However, soil-cement made with granular soilsproduces less shrinkage, but larger cracks spaced atgreater intervals.

Shrinkage and Cracking

Control of Cracking

Compacting at slightly less than optimum moisturecontent

Limiting the fines content in the soil Using interlayers to inhibit propagation of cracks

from the base layer such as providing a surfacedressing layer with PMB or 50-100 mm unboundgranular aggregate interlayer

Delayed surfacing and prolonged curing

Quality control for soil-cement base

Field Testing for quality checks during construction Pulverization Uniformity in mixing Water content Density Cement content (ASTM D5982 may be used to

determine the cement content of freshly mixed soilcement.)

Evaluation soil-cement base

Stiffness Evaluation Falling Weight Deflectometer (FWD) Light Weight Deflectometer (LWD) Soil Stiffness Gauge (SSG)

Field Testing for strength Dynamic Cone Penetrometer (DCP) Mould casting Core cutting

Evaluation soil-cement base

FWD LWD SSG

DCP

Dynamic Cone Penetrometer DCP is an in-situ testing device

used in field exploration andquality control of compactedsoils during construction.

log(UCS) = 3.21 – 0.809log(DN)

UCS = the unconfined compressive strength (kPa), and

DN = the DCP reading (mm/blow)

(McElvaney and Djatnika 1991)

Standards to follow

ASTM- D6951/ D6951M − 18: Standard Test Method for Useof the Dynamic Cone Penetrometer in Shallow PavementApplications

ASTM-D4694−15-Standard Test Method for Deflections with aFalling-Weight-Type Impulse Load Device

ASTM-E2583−15- Standard Test Method for MeasuringDeflections with a Light Weight Deflectometer (LWD)

ASTM-D6758−18 Standard Test Method for MeasuringStiffness and Apparent Modulus of Soil and SoilAggregate In-Place by Electro-Mechanical Method

Moulded Cylinder Strength

Standard Proctor mould and hammerused to make soil-cement specimens

ASTM D 1632 (2007) states that themolded specimen remain in the moldwhile curing in a moist room for 12hours or longer, then it shall beremoved

Once extruded, the specimens areplaced back into the continuous moist-curing room. At the end of the moist-curing period, the specimens aretested immediately after.

Moulded Cylinder Strength

D1633 − 17- Standard TestMethods for CompressiveStrength of Moulded Soil-Cement Cylinders

The cylindrical steel mouldsused had an inside diameterof 2.8 inches (71.1 mm) anda height of 9 inches(229mm).

Core Strength

Cores should be taken on the sixthor seventh day after completionof the soil-cement roadbed for in-place compressive strength testing.

All cores once removed from thein-place soil-cement bed are to beplaced in a plastic bag tominimize moisture loss.

If water was used during thecoring operation, the surface ofthe cores samples shall be let toair dry in the shade for 30minutes before placing them in aplastic bag

Summary

For sustainable development of Infrastructure there is aneed to save the limited natural resources and increaseuse of locally available marginal materials.

Stabilization of the soil using cementitious materials forreplacing the granular layers is a common ecofriendlypractice in most of the countries to save the naturalresource.

Almost all types of soils/granular materials can be usedfor making soil-cement bases, which is a step towardsdevelopment of cost effective rural roads.

References

ACI 230. 2009. Report on Soil Cement. (ACI 230.1R-09), American ConcreteInstitute, Farmington Hills, MI.

ASTM D 559-03 (2015). Standard Test Methods for Wetting and DryingCompacted Soil-Cement Mixtures. ASTM International, West Conshohocken, PA.

Biswal, D. R., Sahoo U. C. and Dash S. R., (2018) “Mechanical Properties of CementStabilized Granular Lateritic Soils”, Road Materials and Pavement Design, Taylor &Francis Pub. (Published online).

George, K.P. 2002. “Minimizing Cracking in Cement-Treated Material for ImprovedPerformance.” Research and Development Bulletin RD123, Portland CementAssociation. Skokie, IL.

Halsted, G.E., Luhr, D.R., Adaska, W.S. 2006. Guide to Cement-Treated Base (CTB).Portland Cement Association. Skokie, IL.

McElvaney, J. and IR. Bunadi Djatnika. 1991. “Strength Evaluation of Lime-Stabilized Pavement Foundations Using the Dynamic Cone Penetrometer.” AustralianRoad Research, Vol. 21, No. 1, pp. 40-52.

Portland Cement Association (PCA). 1971. “Soil Cement Laboratory Handbook.”Engineering Bulletin, Portland Cement Association. Skokie, IL.

Thank you