Use of Naturally Occurring Pozzolans for Road Construction in Tanzania

USE OF NATURALLY OCCURING POZZOLANS FOR ROAD CONSTRUCTION INTANZANIA

Offered for Presentation at the 9th International Conference on Low-Volume Roads,Austin, Texas, June 24-27, 2007

Mbakisya Onyango Graduate Research Associate

Kansas State University,Department of Civil Engineering

2118 Fiedler Hall,Manhattan, KS 66506.

Tel. No. (785) 532-1573Fax No. (785) 532-7717E-mail: [email protected]

Innocent Macha Head

Transportation DepartmentCOWI (T) Consulting, Consulting Engineers and Planners

P. O. Box 1006Dar es Salaam, Tanzania

Tel. No. (255) 744 222036 Fax No. (255)

E-mail: [email protected]

Corresponding author

Christian BuschSenior Pavement Specialist, M.Sc., Ph.D.

COWI A/SParallelvej 2

2800 Kongens Lyngby, DenmarkTel. No. +45 45 97 22 11

E-mail: [email protected]

Submission date: March 29,2006

Word count: 6,947

Key words: Natural pozzolan, Granulated Blast Furnace Slag (Sand-slag)

Onyango, Macha, Busch 1

ABSTRACTThe Pilot Research Study had been conducted in Tanzania to investigate the possibility of usingnaturally occurring pozzolan materials as sand stabilizing agent for road base/subbaseconstruction. The pozzolan material investigated was to be used in the Coastal area of Tanzania,which lacks good road construction materials that meet material specification requirements. TheCoastal area produces mainly sand and some poor quality limestones that are not very suitablefor road construction. Pozzolan samples collected from different parts of Tanzania wereinvestigated. The collected Pozzolan samples were mixed with lime (Ca(OH)2) to stabilize sandthat could be used in a base or subbase course. Laboratory tests were carried out to determineproperties of individual pozzolans and lime-pozzolan-sand mixtures. The compressive strengthand split tensile tests were performed to determine the pozzolan mixtures strength developmentand its suitability for road construction. In this paper, Tanzanian experience with Pozzolanicmaterials will be discussed based on the experience of the Dar-Mlandizi Road Project, whichwas constructed using sand stabilized with blast furnace slag as base course material and thepilot study on the possible use of naturally occurring Pozzolans for road construction. The paperalso highlight the availability of natural Pozzolans in Tanzania, preliminary testing of naturalPozzolans in Tanzania, the follow-up testing of natural Pozzolans in Denmark, and theconstruction of a test road section in Tanzania. The Pilot Study can be considered as an exampleof a successful research on investigating the use of local materials for road construction.

INTRODUCTIONThe primary role of a pavement structure is to support traffic loads and transmit them to thesubgrade soil, after reducing the stresses to levels well below the bearing capacity of the soil. Apavement therefore consists of layers, which performs different primary functions in transmittingtraffic load. These layers may include, (1) wearing /surface course (2) binder course and/or basecourse and (3) subbase course (1). The strength required for construction materials increasesfrom bottom up and the layer thickness is provided depending on heavy traffic volume and thedesign methodology adopted.

Tanzania constructs mainly three types of pavements, flexible, semi-rigid, and unpaved(gravel/earth) roads. More than ninety five percent of paved roads are flexible pavement, havingeither surface treatment or bituminous mix for a surface course placed over a granular unboundor treated (chemically stabilized) base course. The base course is commonly treated usingbituminous mix or penetration macadam (2).

For a pavement with granular base course and 3-10 million ESAL, Tanzania PavementDesign and Materials Manual recommends a 50mm asphalt concrete surface course; 150mmcrushed rock granular base; 200mm subbase from gravel/soil with minimum 4-days soaked CBRof 20% at 95% MDD, laid in top of a subgrade with at least 15% 4-days soaked CBR. For thegranular base, the Manual recommends durable crushed rock, either fresh quarried rock or cleanun-weathered boulders of minimum 0.3m diameter free from soil fines, with Ten Percent FinesValue TFVdry of 110KN and minimum TFVsoaked = 75% TFVdry (2). The granular base coursematerial requirement is hard to meet in some areas of Tanzania, including the Coastal areaswhich have mainly limestone aggregates. In these areas, good road construction materials areobtained from long haul distances resulting in high construction costs.

Due to scarcity of good construction materials, and availability of sand in the coastalarea, sand can be stabilized and used for base or subbase courses. The most commonstabilization methods include sand-cement and sand-asphalt mixtures. Since in Tanzania both


cement and asphalt are expensive, cheaper and durable materials are needed to improve sandproperties to build better base or subbase courses. Granulated blast furnace slag, naturalpozzolan, or fly ash may be other alternatives for stabilization of sandy soils to substitute forgood natural road construction materials.

Granulated blast furnace slag (GBFS) has been used extensively in France to stabilizesand for road construction. This technology has also been used in Tanzania on two constructionprojects. First for the construction of aprons and runways of Dar es Salaam International Airport(DIA) in 1980, and second for the construction of a 56 km road from Dar es Salaam to Mlandizi(Coastal area) in 1999. Assessment of DIA performed in 1997 in preparation for the Dar esSalaam-Mlandizi road project indicated that the runways and aprons constructed using sand-slagmixture was still in good condition 17 years after construction (3). This was one of the factorsconsidered in the adoption of GBFS as base course stabilization materials for the Dar-MlandiziRoad project.

The use of granulated blast furnace slag on Dar-Mlandizi road project initiated theresearch on the possibility of using naturally occurring pozzolans for road construction inTanzania. In 1999, the “Pilot Study for Possible use of Locally Available Pozzolan in Tanzania”was conducted to look on the possibility of using natural pozzolan available in Tanzania for roadconstruction. This was the first study to look at Pozzolan materials with respect to roadconstruction in Tanzania. This paper describes Tanzania's experience on the use of pozzolanmaterials for road construction and outlines the major findings of the Pilot Study.

THE PILOT STUDY ON NATURAL POZZOLANDefinition of TermsNatural pozzolan is a material of volcanic origin which may be defined as; “Essentially siliceousmaterial, which while in itself possessing no cementitious properties, will in finely divided formand in the presence of water react with Calcium Hydroxide (hydrated lime) at ordinarytemperature to form compounds possessing cementitious properties”(3,5,6). Pozzolan occurs inthree different forms; Ash, Pumice and Scoria.

During volcanic eruptions hot ashes containing specific elements are thrown into the airand later on they cool and fall on the ground forming deep layers in their loose form. Thismaterial is mainly referred to as pozzolan. Pumice is white or gray and is highly vesiculatedmaterial, which at the moment of effusion was almost liquid. It has froth-like appearance thatresults from the sudden release of dissolved vapors on solidification. Scoria is also a vesicularpyroclastic material but is composed of heavier ferruginous material lavas and is usually denserand darker in color than pumice (3,5,6).

Historical Background of Natural PozzolanNatural pozzolan is not a new construction material. It was used as Lime-Pozzolan mortar byRomans more than 2000 years ago. During Roman days, pozzolan mortars were used to build allsorts of structures including dams and aqua-ducts, some of which are still existing andfunctioning today. These remaining structures have demonstrated good strength and durabilityproperties of the material. Pozzolan mortars may also have been used by ancient Egyptians forconstruction of the Great Pyramids, which still stand to date (5).

While European pozzolan deposits (since their discovery by the Romans and the Greeks)have been and are still being industrially exploited, primarily by the concrete industry as an


additive to Portland cement, very large and valuable pozzolan deposits remain unexploited inmany developing countries (3).

In Tanzania, studies on pozzolanic materials started as early as 1932 by Imperial InstituteGeological Survey Department of UK (6,7), but were discontinued after the independence ofTanzania in 1961. In 1976 Small Industries Development Organization (SIDO) and InternationalTechnology Development Organization (ITDG), London carried out a research to find a way ofutilizing lime pozzolan mortars as a binding agent to reduce the use of cement in construction,and hence, reduce construction cost of the buildings (8). The Building Research Unit (BRU) alsodid a similar research in 1980 (9). The research projects were concluded by a construction of twodemonstration houses, which 26 years later are still standing. Natural pozzolan in Tanzania isalso used for Portland Pozzolan Cement (PPC) production. The early studies on pozzolanicmaterials in Tanzania were directed to buildings, this is the first study investigating Pozzolan usein road construction.

Background of the Pilot Study - Sand-Slag Base CourseThe background of the Pilot Study for Possible Use of Naturally Occurring Pozzolan in Tanzaniawas the construction of the 56 km Dar-Mandizi Road. The project was designed and supervisedby Danish consulting company, COWI Consulting Engineers and Planners, from 1996 to 2001.

The 56 km Dar-Mlandizi road passes through a coastal area with local coarse aggregatesof too poor quality to be used as pavement base course material. The construction of traditionalflexible pavement with thick asphalt binder and wearing courses on top of a crushed gravel basecourse, seemed to be expensive compared to the construction of a pavement structure that usesfor the base course, the local sand stabilized with blast-furnace slag imported from France. Thesecond solution reduced the thickness of asphalt surfacing and the overall costs of 20% (aboutUS$ 10 million), compared to thick asphalt layer solution, which required hauling of crushedaggregate from a quarry more than 100 km away from the construction site (3,4).

The Dar - Mlandizi road was designed as a semi rigid (composite) pavement, with adesign period of 20 years. The design was based on the SHELL criterion for permissible verticalstrain in unbound materials of 890 x 10-6 at 106 load repetitions. The design also gives provisionto a better load carrying capacity and provides reduction in rate of development of surfaceroughness (4).

The sand-slag mixture used for base course comprised of 12% GBFS, 1% gypsum (asactivator) and the remaining 87% natural sand from a selected source along the road. The mixingprocess was done in a computer controlled mixing plant, which produced a homogeneous mix.The sand-slag mixture of 450mm thick layer was placed in two lifts, the second layer by a paverin order to get the material to the correct levels. The edges were shaped and pre-compacted inone operation. In the field, the mixture takes 7 days to be checked for its strength developmentafter laying the base course. For control, laboratory tests were carried in accordance with theFrench specifications (NF P 98-230-2 and NF P 98-114-2) on 5 x 10 mm cylindrical specimens.The specimens were cured at 20oC and tested on 7, 14, 28, 60, 90 and 180 days for compressivestrength, and 28, 60, 90 and 180 days for split tensile strength test (4).

The advantages of using ground granulated blast furnace slag for road construction includeamong others: use of recycled waste material (GBFS), which has a very low market value andshipping cost, this reduced the total construction cost by 50% as compared to using TanzanianOrdinary Portland Cement, also enabled the use of local materials (sand) along the road. Sand-slag binders are more ductile than cement, resistant to cracking (that plagues Portland cement


bound pavements), no age hardening failure; and it has a self-healing behavior. The fourproperties account for better performance in the field, including longer pavement life. This hasconsiderable effect on the intervals at which investments in road rehabilitation or reconstructionhave to be done. In addition to the four properties mentioned above, the use of alternativematerial contributes to reduction of CO2 emissions since the energy required for the productionof accounts to over 8% of total CO2 emission world wide (4).

The use of GBFS on Dar-Mlandizi Project initiated the research study entitled “PilotStudy for Possible Use of Naturally Occurring Pozzolan for Road Construction” with the view tousing natural pozzolan instead of GBFS for stabilizing sand used for base/subbase course.

Availability of Natural Pozzolan in TanzaniaPozzolanic materials in Tanzania are abundant especially in Mbeya, Arusha, and KilimanjaroRegions (Figure 1) (6,7,8,9). For the Pilot Study, samples of natural pozzolan were collectedfrom these regions for analysis. The preliminary testing included six samples from Arusha,thirteen from Mbeya, and five from Kilimanjaro. The tests included chemical composition andreactivity of the pozzolanic materials with hydrated lime. From the preliminary testing, threesamples from Arusha, six from Mbeya and two from Kilimanjaro were selected for furthertesting.

The Arusha Pozzolan deposits, located on the West slopes of Mount Meru are notquantified, but the area is considered resourceful. Some of these deposits were used in early1980’s for the pozzolan-lime project by SIDO. Figure 2 shows the first pozzolan deposit used bySIDO and BRU from 1976 to 1981. The deposits in Mbeya are mainly used by Mbeya CementCompany (MCC), and are roughly quantified to about 500,000 tons of pozzolan but the areahaving this material is much bigger (potentially more than four times) than the quantified area.Pozzolan deposits identified in Kilimanjaro region are hardened pumice, reddish in color, whichare cut into blocks and used for house construction. Other deposits are in a form of hardenedrock. A Cement Company in the area is researching on the possibility of using this material forcement production. In general, Kilimanjaro deposits are believed to be from the old volcanicdeposits and have hardened, which makes it hard to work with for roads construction. Highenergy is needed for grinding to sizes usable for roads construction.

Laboratory Investigation of Properties of Pozzolan Stabilized SandNatural pozzolan samples collected were chemically tested at the Southern and Eastern

Africa Mineral Centre (SEAMIC) in Tanzania, to determine their chemical composition. Someof the samples were sent to Denmark for Differential Thermal Analysis (DTA) to determinepotential reactivity with lime and X-ray Diffraction for determination of glass content. The testscarried out in Denmark contributed to the selection of pozzolan samples for further analysis.

The following laboratory tests were carried out on the selected individual pozzolansamples to determine their physical properties:

· Grading and Hydrometer analysis AASHTO T88-93;· Atterberg limits AASHTO T89-96 and T90-96;· Methylene blue value, French Specification, NFP 94-068;· Organic content AASHTO T267-86;· Sand Equivalent Value AASHTO T176-86; and· Specific Gravity AASHTO T100-95.


The selection of the mixtures was based on the experience from the Dar Mlandizi roadproject as reference and the reactivity of respective pozzolan materials. The mixturecompositions adopted for testing are as shown in Table 1 (4). The samples tested using themixtures composition in Table 1 includes;

· 3 samples from Oldonyo sambu Arusha, 1-O, 2-O and 4-O;· 6 samples from Mbeya, 1b-M, 2b-M, 4-M, 9-M, 10-M and 14-M; and· 2 samples from Kilimanjaro, 2-K and 4-K.

Mixture optimization was performed according to the reactivity tests carried out andusing the Dar-Mlandizi road sand-slag mixture as reference. ASTM, AASHTO, and Frenchstandards were referred.

Sand used for the trial mixes was the same sand used for base course construction of Dar-Mlandizi road. Lime manufactured in Tanga, Tanzania was used, when tested for purity atSEAMIC the results were 92.3% of Ca(OH)2, ASTM specifies a minimum requirement ofCa(OH)2 as 90%. For the selected Lime-Pozzolan-Sand mixtures in Table 1, the following testswere carried out:

· Grading and Hydrometer analysis, AASHTO T88-93;· Modified Proctor, AASHTO 180-95;· California Bearing Ratio (CBR), AASHTO T193-93;· Unconfined Compressive Strength (Rc), AASHTO T22-92 (1996); and· Split Tensile Strength (Rt), AASHTO T198-93 (1996).

Table 2 tabulates a summary of the results obtained after testing the Lime-pozzolan-sandmixtures. The un-soaked California Bearing Ratio (CBR) of all the pozzolan samples was morethan 50% the actual values ranged from 66% to 150%. The Maximum Dry Density (MDD)varied between 1850 and 2040 kg/m3 with optimum moisture content (OMC) between 7 and10%. The variation is due to difference in fines content of the pozzolans.

The strength results of the mixtures show that all pozzolans except 9-M, 2-O and 2-K at28 to 60 days achieved a compressive strength much similar, higher or much higher than thereference sand-slag (GBFS) mixtures used on the Dar Mlandizi project. The sand-slag mixturehad compressive strength development 0.86 and 1.33 MPa for 28 and 60 days respectively. Mostof samples from Arusha had the highest compressive strength development, some samplesdeveloped compressive strength as high as 4.33 and 5.19 MPa for 28 and 60 days respectively.Mbeya samples had much lower or slightly higher compressive strength developed as comparedto the sand-slag compressive strength of Dar-Mlandizi road. The similar trend was observed forthe split tensile strength test results.

The results of most samples from Mbeya and Arusha indicated that the sand-pozzolanmixtures could be used for road construction. The compressive strength development for mostmixtures after 180 days was higher than the 180 days strength development of sand-slag (GBFS)mixture. Samples from the Kilimanjaro pozzolans had low strength development and they needhigher grinding energy if they are to be used, therefore, are not recommended for roadconstruction. Figures 3 and 4 shows a summary of compressive strength and split tensile resultsobtained from the Pilot study.

The results also indicate that several pozzolans occurrences in Tanzania fulfill therequirement for use as a binder material for road construction as well as other possible uses inthe building industry. From the results, it is clear that natural pozzolan could be used for roadconstruction but there is a need for more testing and for construction and monitoring of a pilot


road which can validate the findings. A one km section has been constructed near Morogoro fora preliminary evaluation of the performance of base course stabilized by natural pozzolan.

FIELD VALIDATION OF NATURAL POZZOLAN STABILIZATIONPost Pilot Study Testing in DenmarkPrior to construction of a test section, further testing was carried out in the Danish Road TestingMachine (RTM) in Denmark. The RTM is a pavement testing facility, capable of applying amaximum dual wheel load of 60kN at a maximum speed of approximately 25km/h, with loadrepetitions of roughly 5,000 to 10,000 per day depending on the operational speed. The lateralposition of the wheel can be automatically controlled during testing to give a desired transversewheel load distribution (wander). The RTM is enclosed in a climatic chamber which was used tosimulate tropical conditions close to those applicable in Tanzania. The RTM is instrumented withsensors, which have been developed through previous research projects. The sensors includeAsphalt Strain Gauges, Soil Deformation Transducers, Soil Pressure Cells, Soil Pore PressureSensors and Thermocouple probes to monitor temperature (3).

The selected Arusha Pozzolan sample was transported from Tanzania to Denmark. Sandsimilar to that used in the Pilot Study with lime from Denmark were used to make a lime-pozzolan-sand mix for testing in the RTM. Results obtained from this test are not been reportedin this paper, but were referred in the design of the test road section constructed in Tanzania.

Design of Pozzolan Stabilized Base CourseNatural Pozzolan have never been used for road construction in Tanzania. Therefore, it wasimportant to construct a pilot road in order to assess its performance. COWI ConsultingEngineers and Planners included a test section of about one km long with lime-pozzolanstabilized base course in the design of 129 km Chalinze-Melela road project.

The Tanzania Pavement Design and Materials Manual provides a design guide forcemented base course, not specifically pozzolan base course. The recommended unconfinedcompressive strength (UCS) of the cement treated base course materials ranges from 0.5 to2.0MPa depending upon the design traffic load. The design catalog given by the PavementDesign and Materials Manual is shown in Table 3 for three traffic classes of low volume roads.COWI combined the provisions given by the Tanzania Pavement Design and Materials Manualand the United Kingdom overseas Road Note (RN) 31 to come up with a design which was morefavorable (Table 4) (10).

Materials that could be used for Pozzolan-lime stabilized bases includes: (10)· Course sand 0/2mm or gravel, which is the main component of the mixture;· Fine, silty sand 0/1 mm, a so called “grain size adjuster” or laterite;· Pozzolan from Arusha or Mbeya regions which proved to be more active during the Pilot

Study testing; and· Hydrated lime.

The number of materials to be used indicates the need for a mix design to obtain exactvolume of for the materials to be mined, transported and used for construction. The mixturetherefore to be determined and should conform to Chapter 7 of the Pavement Design andMaterials Manual.


Construction and Performance of a Test SectionThe Chalinze-Melela Road project was a reconstruction project. The design of a test section,therefore, utilized the existing base course mixed with pozzolan to the ratios oflime:pozzolan:existing base of 1.8:8.5:90. Lime-pozzolan mixture was mixed in place with theexisting base, the Wirtgen reclaimer was used. The construction process included adding lime-pozzolan mix to the existing base, mixing and adding water to OMC, compacting the mixedmaterials, shape and compact the surface to a straight transverse profile and required cross fall,seal the surface, coring for checking thickness, density and compressive strength.

The test section constructed using the existing base materials stabilized with lime-pozzolan (pozzolan from Arusha deposits) mixed in place. The existing base materials containaggregates, this resulted in minimal or no shrinkage cracks, which were experienced with sandslag on Dar- Mlandizi Road project. Cores were taken to ensure there was satisfactory strengthdevelopment. The performance of the pavement, one year now since construction, is very good,no shrinkage cracks or any types of failures have been observed. The section will be monitoredas a base/reference for future developments.

CONCLUSION· The study on the possible use of natural occurring pozzolans in Tanzania can be

considered as an example of a successful research on investigating the use of local materials forroad construction. Major findings from this research indicate a possibility of using naturalpozzolans for road construction, however further research is needed in order to come up withdesign guidelines, technical specifications and maintenance guidelines for repair of pozzolanbases possibly after more experience have been gained (10).

· The compressive strength of several natural pozzolans investigated in the pilot studyshow higher strength development as compared to sand-slag mixtures used on Dar-Mlandiziproject with similar binder contents. For example, the binder content of pozzolan-lime can bereduced for similar or even higher strength results compared to that obtained from sand-slagmixture. This is an indicative property of high strength development in natural pozzolans andqualifies it for consideration as sandy soil stabilization materials for road construction.

· A detailed geological investigations and material testing is required for development of alocal mining industry. Available pozzolan deposits need to be quantified and the packaging andsupply process of pozzolan materials could be commercialized to involve local communitiesaround areas where pozzolan is abundant (10).

· Natural Pozzolan could be used as a resource in place of energy demanding products suchas the Portland cement. The use of pozzolan supports sustainable development as a key criterionin the criteria for development projects. This concept can contribute to an end of the traditionalexpensive and non-feasible road projects, which has been a barrier to the sustainableimprovement/reconstruction of many road networks (3);


ACKNOWLEDGEMENT

1. The Danish International Development Agency (DANIDA) for funding the research projectsinvestigating the possibility of using natural pozzolans for road construction

2. COWI Consulting Engineers and Planners for giving us an opportunity to work on the pilotStudy team

3. The Pilot Study team members for valuable inputs. Each one played an important role in theprocess to come up with the findings.

REFERENCES1. Bent Thagesen. Highway and Traffic Engineering in Developing Countries. Chapman &

Hall, UK, 1996.2. The United Republic of Tanzania, Ministry of Works. Pavement and Materials Design

Manual. Allkopi AS, Oslo Norway, 1999.3. Eriksen, K., Zhang, W., Thogersen, F and Macdonald, R.A. Feasibility of Pozzolan –

Stabilized Pavements in Developing Countries. In Technology Transfer T2 ConferenceProceedings, Arusha, Tanzania, May 2001.

4. COWI Consulting Engineers and Planners. Pilot Study for Possible Use of Locally AvailablePozzolan in Tanzania: Summary Report to the Ministry of Works. Dar es Salaam, Tanzania,2000.

5. Rugunda, R. Using the Secrets of the Great Pyramid in Modern-day Infrastructure. Dar esSalaam, Tanzania (Unpublished).

6. Koeppel, W. Compilation of Raw material Occurrences and Their Suitability for BuildingMaterials Purposes: Kilimanjaro Region. BRU Report, Dar es Salaam Tanzania (undated).

7. Koeppel, W. Compilation of Raw material Occurrences and Their Suitability for BuildingMaterials Purposes: Mbeya Region. BRU Report, Dar es Salaam, Tanzania (undated).

8. Sakula J. H. and Sauni, J. T. M. The SIDO Lime - Pozzolana Project. In Pozzolana andPumice as Construction Materials” Department of Geology, University of Dar es Salaam,1987.

9. Mtui, A. L. and Kawiche, G. M. Portland Pozzolan Cement. Working Report No. 31, BRU,Dar es Salaam, Tanzania 1983.

10. COWI Consulting Engineers and Planners. Pozzolan Lime Stabilized Low Volume: A reportto DANIDA. Dar es Salaam, Tanzania, 2004.


LIST OF TABLES

TABLE 1 Mixture Abbreviations and Composition

TABLE 2: Summary of Compressive and Tensile Strength Results

TABLE 3 Design Catalogue for Subgrade CBR >15%

TABLE 4 Design Catalogue for Subgrade CBR >15% as Improved by COWI

LIST OF TABLES AND FIGURES

FIGURE 1 Location of Pozzolan Sample Sites

FIGURE 2 First Pozzolan Deposit used by SIDO 1976 to 1981

FIGURE 3 Compressive strength results

FIGURE 4 Split tensile test results


TABLE 1 Mixture Abbreviations and Composition

SN. Mixture type Mixture Ratio1. XA12 88% Area D Sand + 9% Selected Pozzolan + 3% Hydrated lime.2. XA16 84% Area D Sand + 12% Selected Pozzolan + 4% Hydrated lime.3. XA16(G) 83% Area D Sand + 12% Selected Pozzolan + 4% Hydrated lime +

1% Gypsum.4. XB12 88% Area D Sand + 10% Selected Pozzolan + 2% Hydrated lime.5. XB12(G) 87% Area D Sand + 10% Selected Pozzolan + 2% Hydrated lime +

1% Gypsum

NOTEXA12 = Essentially 12% Pozzolan-lime mixture as cementing materials;XA16 = Essentially 16% Pozzolan-lime mixture as cementing materials;XA16(G) = Essentially 16% Pozzolan-lime mixture as cementing materials plus 1% gypsum;A or B defines lime:pozzolan ratio, A 1:3 and B 1:5.

TABLE 2: Summary of Compressive and Tensile Strength Results (4)

CBR Proctor Compressive Strength (Mpa) Tensile Strength (Mpa)Mix

(%)MDD

(kg/m3)OMC(%)

Rc 7 Rc 14 Rc 28 Rc 60 Rc 90 Rc 180 Rt 28 Rt 60 Rt 90 Rt 180

1-0 (XA12) 109 2034 9.2 1.23 1.33 1.58 2.02 2.05 2.74 0.26 0.29 0.26 0.351-0 (XA16) 66 1988 9.6 2.94 3.73 4.22 5.06 5.17 7.38 0.68 0.81 1.02 1.05

1-0 (XA16G) 98 1999 8.7 3.00 3.69 4.33 5.19 5.13 6.10 0.70 0.82 0.65 0.991-0 (XB12) 105 2026 8.7 2.15 2.53 2.71 3.35 3.45 3.74 0.52 0.52 0.61 0.70

1-0 (XB12G) 109 2000 9.2 2.19 2.53 3.17 3.49 3.49 3.90 0.41 0.55 0.63 0.692-0 (XA12) 68 1860 9.6 0.12 0.13 0.20 0.41 1.07 2.76 0.01 0.04 0.13 0.462-0 (XA16) 82 1893 9.4 0.24 0.32 0.64 1.84 3.00 4.12 0.07 0.36 0.50 0.85

2-0 (XA16G) 95 1850 10.6 0.19 0.32 0.70 1.97 3.29 5.21 0.06 0.27 0.54 0.822-0 (XB12) 99 1910 9.6 0.11 0.13 0.23 0.84 1.36 2.92 0.02 0.11 0.21 0.48

2-0 (XB12G) 103 1910 10 0.12 0.17 0.31 0.92 1.97 2.92 0.03 0.11 0.24 0.484-O (XA16) 104 2025 9 3.11 3.60 4.17 4.27 4.59 4.83 0.72 0.89 1.03 0.90

1b-M (XA16) 92 1850 10 0.30 0.47 0.99 2.02 2.97 4.69 0.10 0.26 0.43 0.852b-M (XA16) 84 2020 8.4 0.54 1.56 2.15 3.12 4.38 4.98 0.31 0.59 0.64 0.694-M (XA16) 88 1970 7.4 0.22 0.36 0.96 1.84 3.12 5.73 0.08 0.22 0.46 0.889-M (XA16) 85 2020 8.2 0.13 0.13 0.13 0.18 0.16 0.24 0.01 0.01 0.01 0.0210-M (XA16) 98 1895 10 0.22 0.42 0.73 1.67 2.56 4.81 0.10 0.21 0.42 0.7514-M (XA16) 150 1995 6.8 0.27 0.36 0.71 1.15 2.14 4.36 0.07 0.17 0.33 0.702-K (XA16) 89 2040 6.6 0.17 0.17 0.34 0.43 0.50 0.94 0.03 0.06 0.08 0.124-K (XA16) 86 1975 8.5 0.57 1.03 1.13 1.30 1.89 2.13 0.16 0.24 0.24 0.42

GBFS 0.39 0.62 0.86 1.33 0.13 0.20 0.26

TABLE 3 Design Catalogue for Subgrade CBR >15% (2)

LayerTraffic (million ESALS)

<0.2 0.2 – 0.5 0.5 – 1.0Surface ST

CM

G25

DBST ST

CM

G45

DBST ST

C1

G45

DBSTPozzolan-limeStabilized base 150mm 150mm 150mmSubbase

150mm 150mm 150mm

NOTES:ST = Surface treatmentDBST = Double surface treatmentCM = Cemented base material with min. compressive strength of 0.5MPaC1 = Cemented base material with min. compressive strength of 1.0MPa


TABLE 4 Design Catalogue for Subgrade CBR >15% as Improved by COWI (9)

LayerTraffic (million ESALS)

<0.2 0.2 – 0.5 0.5 – 1.0Surface ST

Pz2

G25

DBST ST

Pz2

G45

DBST ST

Pz2

G45

DBSTPozzolan-limeStabilized base 150mm 150mm 150mmSubbase

150mm 150mm 150mm

NOTES:ST = Surface TreatmentDBST = Double surface treatmentPz2 = Lime pozzolan with 2 MPa 28 day compressive strengthG25 = Gravel with min. CBR = 25%G45 = Gravel with min. CBR = 45%


FIGURE 1 Location of pozzolan sample sites


FIGURE 2 First pozzolan deposit used by SIDO from 1976 to 1981

7 to 180 days compressive strength

00.5

11.5

22.5

33.5

44.5

55.5

66.5

77.5

8

1-0(X

A12)

1-0(X

A16)

1-0(X

A16G)

1-0(X

B12)

1-0(X

B12G)

2-0(X

A12)

2-0(X

A16)

2-0(X

A16G)

2-0(X

B12)

2-0(X

B12G)

4-O(X

A16)

1b-M

(XA16

)

2b-M

(XA16

)

4-M(X

A16)

9-M(X

A16)

10-M

(XA16

)

14-M

(XA16

)

2-K(X

A16)

4-K(X

A16)

GBFS

Sample No. and composition

Com

pres

sive

stre

ngth

(MPa

)

Rc 7Rc 14Rc 28Rc 60Rc 90Rc 180

FIGURE 3 Compressive strength results


28- to 180 days Tensile strength

0

0.2

0.4

0.6

0.8

1

1.2

1-0(X

A12)

1-0(X

A16)

1-0(X

A16G)

1-0(X

B12)

1-0(X

B12G)

2-0(X

A12)

2-0(X

A16)

2-0(X

A16G)

2-0(X

B12)

2-0(X

B12G)

4-O(X

A16)

1b-M

(XA16

)

2b-M

(XA16

)

4-M(X

A16)

9-M(X

A16)

10-M

(XA16

)

14-M

(XA16

)

2-K(X

A16)

4-K(X

A16)

GBFS

Sample no. and strength

Tens

ilest

reng

ht(M

Pa)

Rt 28Rt 60Rt 90Rt 180

FIGURE 4 Split tensile test results

Use of Naturally Occurring Pozzolans for Road Construction in Tanzania

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