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Tensile and compressive strength of some stabilised road bases in Kenya

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Tensile and compressive strength of some stabilised road bases in Kenya by C. R. Jones and H. R. Smith TRANSPORT and ROAD RESEARCH LABOWTORY Department of the Environment Department of Transport SUPPLEMENTARY REPORT 623 TENSILE AND COMPRESSIVE STRENGTH OF SOMESTABIMSED ROAD BASESIN ~NYA by C R Jones and H R Smith The work described in ths Report forms part of the progamme carried out for the OverseasDevelopment Administration, but any views expressed are not necessady those of the Administration OverseasUnit Transport and Road Research Laboratory Crowthome, Berkshire 1980 ISSN 0305–1315 CONTENTS Abstract 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Introduction Selection of the sites Position and method of cutting the samples Pavement investigation tests hvement surface measurements @tting the samples for testing timpression and tensfle tests 7.1 Unconfined compression test 7.2 ~rect tensfle test Results 8.1 Removal of the samples from the road 8.2 Effect of traffic loading on the direct tensfle strength 8.3 Comparison between samples t&en from the verge-sidewheelpath and between the wheelpaths 8.4 Relationship between the unconfined compressive and direct tensfle strength of the samples discussion Conclusions Achowledgements References Rige 1 1 1 2 2 2 2 3 3 3 3 3 4 4 4 4 5 6 6 (C) CROWN COPYNG~ 1980 Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged TENSILE AND COMPRESSIW STRENGTH OF SOME STABILISED ROAD BASESIN KEWA ABSTRA~ This report describes the measurement of the direct tensfle and unconfined compressive strength of samples cut from stabfised roadbases in Kenya. The test methods used are described, and the strength of the samples is compared with the performance of the roads. The report concludes that although the bases have lost tensfle strength in service, they have not suffered serious structural damage and with routine maintenance these pavements should continue to perform satisfactorily. 1. INTRODUCTION Previous research at pflot-scde has indicated a relationship between the cracking of a sofl+ement roadbase ad the tensde strength of the stabtised material at the time of initial trafficking 1. If the base material is weak, the initial cracks are found to be narrow and closely spaced in contrast to the large but widelyspaced cracks that result if the stabtised layer is strong at the time when it is first stressed. k 1973a cooperative prograrnme of research was undertaken by the OverseasUnit and Department of (Iti Engineering at the University of Nairobi to measure the strength of efisting stabtised roadbases at selected road sites in Kenya to help to assessthe condition of the pavements and their performance in relation to the traffic carried. Transport and Road Research bboratory staff were responsible for the selection of the road sites and for obtaining samples of the roadbases. Staff from the Univemity of Nairobi were responsible for the preparation and testing of the samples. 2. SELECTION OF THE SITES The samples of stabfised base material were taken from sections of road that were the subject of another study of road strengthening, apart from one site which was on a new road. The sites were located on roads of differenl agesthat had carried different amounts of traffic at the time of sarnphg. Det* of the location of the sites ad the stabihsed roadbases are given in Table 1. The deterioration and traffic loading of some of these sections had been motitored prior to samphg and is being continued subsequently. As the location of the sites ranged from the M@ands of Kenya to sea level, the rainfafl and subgrade SOUS vary considerably. Dettis of annual rainf~, subgrade soils and the dates of samphg are given in Table 2. 3. POSITION AND METHOD OF CUTTING THE SAMPLES The number of chainages at which the stabtised base was sampled varied according to the length of each site (see Table 2). On Sites 1,3,4 and 6 four ‘blocks’ of stabfised material were removed at each of the selected chainages, one from the verge-sidewheelpath and one from between the wheelpaths in each lane (see Figure 1). These locations were selected to see whether differences could be detected between the material extracted from the most heatiy-trafficked part of the pavement (the verge-sidewheelpath) and materird extracted from the least trafficked part of the pavement (between the wheelpaths). On Site 2, a dual carriageway road, blocks were taken at one chainage ordy, from the verge-sidewheelpath and offside wheelpath, and from between the wheelpaths of one slow kme. On Site 5 ody four blocks were removed, one from between the wheelpaths in each lane at two chainages. The blocks were cut from the road using a petrol engined concrete saw (Hate 1) which had been extensively modified for use in dusty conditions. Circular steel and Carborundum blades were used for cutting. Water could not be used as a lubricant because of the possibtity of softening the weaker pavement materials. btting was therefore carried out extremely slowly to avoid damaging the stabfised materials. Four or five samples were cut at each block location. These were approximately 75 mm wide, 200 mm long and deep enough to include the fi~ depth of the surfacing and roadbase (see Hate 2). By cutting a space between each sample and applfig pressure at the interface between the stabfised base and unstabfised sub-base it was possible to ‘shale’the sample from the sub-base. Once removed the samples were wrapped in polythene to preserve their moisture contents and placed in boxes tined with plastic foam sheeting to protect them during transit to the laboratory. 4. PA~MENT INSTIGATION TESTS After the removal of the stabifised base samples, pavement investigation tests were carried out on the subsequent pavement layers. Measurements of layer thickness, moisture content and in-situ CBRvrdues were made. The results are summarised in Table 3. Site 4 has been divided into two sub-sites because of the significant difference between the subgrade strengths of the two parts. In-situ CBR measurements could not be taken on the samples of roadbase prior to removal because the samples would have been damaged. However CBR and moisture contents were measured at locations near the blocks and the results are reported in Table 4. 5. PA~MENT SURFACE MEASUREMENTS Measurements of the transient deflection, rut-depth and cracking were made at rdlsites. Tables 5 and 6 show the mean transient deflection and the rut-depth measured under a 2 metre straight edge at the time of srunphg the stabfised base. There were no significmt areas of surface cracking at any of the sites at the time of samphg. 6. CUTTING THE S~LES FOR TESTING Figure 2 shows the appearance of a sample after it was removed from the road. Two more cuts had to be made in the laboratory before the sample could be tested. These cuts were made with a bench saw using steel and Carborundum blades. To provide adequate restraint during cutting, the sample, stfll wrapped in polythene sheet, 2 wasset in a cement sand mortar. This restraint was necessary to prevent the blade from breaking material from the face of the specimen and thus causing an irregular cross-section. The top of the road surfacing of the sample wasleft flush with the top of the modd and the mortar was Wowed to parti~y cure around the remaining fac(!s. The top of the road surfacing was then used as a reference for the two cuts shown in Figure 2 wfich were made through both the mortar and the sample. A third cut was necessary with the samples that were to be tested in compression to reduce the height: width ratio to 2:1. 7. COMP~SSION AND TENSILE TESTS The samples were tested for their tensfle and compressive strength along the long axis of the sample. 7.1 Unconfined compression test End plates were attached to the samples using plaster of Paris to ensure that the compressive load was apptied along the axis of the sample. The square steel end plates, 75 mm x 75 mm x 5 mm, were mounted on the sample in a rectangular steel mould and were held in place by a turn screw w~t the plaster of Paris set as shown in Figure 3. &fore testing, the cross-section of the sample was measured with vernier crdipers. The mean of three measurements of the cross-section was used to compute the compressive strength. The load was apptied gradudy in a press to fdure using a 50 kN capacity load ceflto measure the load. The Kenya Wstry of Works specify that stabtised roadbase material should attain an unconfined compressive strength of 1.8 N/mm2 after 7 days curing and 7 days immersion in water. These tests are usufly camied out with 100 mm x 50 mm diameter cylindrid samples. Athough cyhdricd specimens could not be prepared from the samples of base extracted from the road previous wor# has shown that rectan~ar samplefi tith a stiar height: width ratio give comparable values of unconfined compressive strength. Hence the samples were cut with a height: width ratio of 2:1. 7.2 Direct tensile test A polyester resin wm used to attach the samples to end caps as shown in Figure 4. The an~e plates werl; slotted to allow the sample to be positioned centr~y with respect to the apptied load. The top cap was attached to a rigid steel frame through a universal couphg and a steel container was attached to the bottom plate dso through a universal couphng. Dry sand was then slowly poured into the container unti the sample fractured. After ftiure the container, the sand and the lower Mf of the sample with the bottom end cap were weighed and the cross-section at the fracture measured with vernier ctipers. 8. WSULTS 8.1 Removal of the samples fmm the road Where the direct tensde strength of the stabtised roadbase wasless than 0.06 N/mm2 the samples were difficult to remove and test without damage. In such casesit was not possible to differentiate between sampli:sthat were cracked prior to the cutting operation and those wfich were cracked by the motion of the blade. 3. Figure 5 shows that fewer samples were successfu~y removed from the road and tested at Sites 3 and 6 and block Nos. 1–12 at Site 4. Block Nos. 13–16 at Site 4 have been separated from Block Nos. 1–12 in Figure S because they have significantly higher tensfle strength. The direct tensfle strength quoted for each site is a mean value for d the direct tensile tests that were successfu~y carried out. The mean direct tensile strengths for Sites 3,4 and 6 are overestimated because the samples wtich were too weak to be tested have not been included in the calculation of the mean strength. 8.2 Effect of traffic loading on the direct tensile strength At two sites a comparison can be made between the tensfle strengths of samples taken from the same site which have experienced different traffic loadings. The direct tensde strengths of samples taken from the verge-side wheelpaths and the estimated cumulative traffic loadings at Sites 3 and 4 are shown in Table 7. At these sites, where there was a considerable difference in traffic loading between the two lanes, the samples taken from the more heatiy trafficked lane had higher tensfle strengths. It was not possible to make accurate estimates of the traffic loadings at the other sites because data were not avtiable. 8.3 Comparison between samples taken from the veqe-side wheelpath and between the wheelpaths Table 8 shows how the tensfle strength of blocks taken from the verge-side wheelpath compares with the strength of those taken from the adjacent position between the wheelpaths. The number of samples from each block tested in tension varies because where there waslarge scatter in the values of tensfle strength additional tests were carried out. Mso a number of samples fractured prior to testing as described earher. The comparison shows that the roadbases are not significandy weaker in the verge-side wheelpath than in the position between the wheelpaths. Detds of the samples that fractured prior to testing are given in Table 9. 8.4 Relationship between the unconfined compressive and direct tensile strength of the samples The unconfined compressive strength and the direct tensfle strength of afl the samples tested are plotted in Figure 6. Each point represents the mean strength of samples taken from one block. The four blocks taken from Site Sare considerably stronger than the other blocks for two reasons. Firstly the corralgravel material at this site formed an extremely dense md mechanica~y stable base. Secondy the samples were taken before the road was heatiy trafficked and consequently no deterioration of the base due to traffic wotid have occurred. Figure 6 shows that the direct tensfle strength does not increase significantly with an increase in unconfined compressive strength. 9. DISCUSSION The road pavements at Sites 3 and 4 conform closely to the pavement design recommendations suggested in Road Note 314 for a traffic loading of 2.5 x 106 equivalent standard ties. Both these sites have now carried considerably more traffic than this but there has been no evidence of serious structural failure. 4 Traffic and tie-load &ta up to the times of samphg for Sites 1,2 and 6 is not avdable. Site 1 has been open to traffic for approximately ten years, Site 2 for fourteen years and Site 6 for four years. At the time of sampkg there was no evidence of base fdure at any of these sites. Revious work by the authors shown in Figure 7 indicates that typical gravek h Kenya stabfied with 4.5 per cent of cement attain a direct tetie strength of approximately 0.1 N/mm2 after four hours curing. These tests were carried out on briquette samples5 using material which passed a 5 mm sieve compacted at maximum dry density6 (2.5 kg rammer method). The values of direct tensfle strength obtained in tiese tests may overestimate to some extent the strength of the gravelin the road, however the indications are that the direct tetie strengths of the samples cut from the road are probably considerably lower than they were soon after construction. Revious work7 has shown that for laboratory prepared clay+ement-mixtures the ratio beween the direct tende strength and unconfined compressive strength varies between 1:3.3 and 1:6.2. The fact that there was no sitiar relationship between direct tensfle and unconfined compressive strengths for tie samples from the roads indicates that it is hkely the roadbases were cracked. Further confirmation of this is provided by the low vrduesof direct tensfle strength of the samples extracted from the roads. The cracks are probably caused by traffic during the early fife of the road. The fact that the results do not show any relationship between direct tensfle strength and cumulative traffic loading indicates that the growth of cracking probably reduced the tensfle strength at an early age, and subsequent trafficking has had fittle effect on the tensfle strength. The high values of transient deflection measured on some of the sites as shown in Table 5 indicate that these roadbases are no longer acting as rigid layers but are acting flexibly. Uspite the low direct tensile strength of the samples the results summarised in Tables 4 and 6 show that the bases stti had mean CBRvaluesin excess of 100 per cent and that very tittle deformation or surface crackirlg had occurred at any of the sites. It thus appears that although the bases contain numerous fine cracks there is sufficient mechanical interlock to provide the strength necessary to carry the traffic over the strong subgrad~; 10. CONCLUSIONS 1. The tensfle tests showed that the majority of the roadbase samples had a lower direct tensfle strength thml would be expected of such material soon after construction, nevertheless the roadbases were stfi carrying the traffic loads satisfactory. 2. The tests showed that the tensfle strength of the samples from the more heatiy-trafficked parts of the pavements was not less than the strength of the samples from the fighter-trafficked areas. 3. There was no correlation between direct tensfle and unconfined compressive strengths for the roadbase samples. 11. ACKNOWLEDGEMENTS This study formed part of the research programme of the OverseasUnit (Unit Head: J N Buhan) of the Transport and Road Research bboratory, United Kingdom. The authors wish to thak Professor R B L Smith and the Department of CivflEngineering of the University of Nairobi for their support and practical help throughout the study. Thti are *O due to M the locdy employed staff for their help during the study. The cooperation of the Wvernment of the Repubtic of Kenya is gratefu~y achowledged for dewing the conduct of field experiments on a public road. 12. REFERENCES 1. 2. 3. 4. 5. 6. 7. BOFINGER, H E and G A SULHVAN. An investigation in soti+ement bases for roads. Department of the Environment, RRL Report LR 379. Crowthome, 1971 (Road Research Laboratory). S~TH, H R and C R JONES. Measurement of pavement deflections in tropical and sub-tropical ctimates. Department of the Environment Department of Transport, T~L Report LR 935. Crowthorne, 1980 (Transpofi and Road Reseuch hboratory). SYMONS,I F. The effect of she and shape of specimen upon the unconfined compressive strength of cement-stabfised rnatenb. Magazine of concrete research, Vol 22, No. 70, March 1970. TRANSPORT AND ROAD RESEARCH LABORATORY. A guide to the structural design of bituminoussurfaced roads in tropical and sub-tropical countries. Department of the Environment, Road Note No. 31. 3rd edition. bndon, 1977 (H M Stationery Office). BOFINGER, H E. The measurement of the tenstie properties of sofl-wment. RRL Report LR 365. Crowthorne, 1970 (Road Research Laboratory). BMTISH STANDARDS INSTITUTION. Methods of test for stabtied sofls. London, 1975 (British Standards Institution). Minist~ of Transport, British Stan&rd 1924:1975. BOFINGER, H E. Sofl-cement as a ri~d pavement material. Unpublished PhD ~esis, University of @eensland, 1968. 6 T~~ 1 hcation of the sites and detds of the stabfised base Site No. I bcation I Road base material I Nominal per cent and type of stabfiser 1 A104 90 h north of NAuru Gravel 6% be at Tirnboroa 2 I A2 Thik bound carriageway at Ruartia I Gravel I 7% cement 3 A109 132 h south of Nairobi at Emati Gravel 4% cement 4a&b A109 356 h south of Nairobi at Maungu Salty clay sand 4% cement 5 A14 40 b south of Mombasa near Mwabungu Coral 5.3% cement 6 A14 62 h SOUth of Mombasa near Ramisi Gravel 5% cement ....... m TAB~ 2 Sampkg dettis, annual rainfti and subgrade type Site No, 1 2 3 (B1OC:I-8) (Bloc#9-16) 5 6 Date of samphng No. of chtinages at which samples tken February 1975 September 1975 June 1975 February 1976 November 1975 November 1975 August 1974 September 1974 3 1 3 4 2 3 Approximate annual rainfd (mm) 1300 700 540 300 300 1100 1200 Description Red clay Red clay ~ayey sflt Sflty clay sand Sflty clay sand Weflgraded sand/sandy clay WeHgraded sand Ntails of subgrade Uquid Mt (per cent) 88 70 39 33 26 -/42 — Hastic index @er cent) 43 37 15 17 13 Non-plastic/22 Non-plastic tinear shrinhge @er cent) 21 17 9 10 8 –/13 ““,,,,,......,,.,.. T~LE 3 Pavement investigation results ~chess Moisture content In-situ CBR Site No. No. of tests Pavement layer (m) (per cent) ~er cent) Mean Range Mean Range Mean &ge Roadbase 122 100–140 – i Sub-base — — — 1 12 118 60–1 50 16.5 14.9–17.8 >75 42–> 100 Subgrade — — 30.2 20.5–35.4 26 8A2 Roadbase 161 155–170 – — — — 2 3 Sub-base 206 160–250 16.8 15.7–18.9 >68 40–> 100 Subgrade — — 27.5 27.2–27.7 15 6–28 Roadbase 143 120–160 – — — — 3 12 Sub-base 130 75–250 17.0 10.2–24.0 42 12–90 Subgrade — — 19.2 16.0–21.1 22 15–28 4a Roadbase 120 110–130 – — — — (Block 1-8) 8 timpacted subgrade 91 50–120 9.8 7.8–11.9 42 20–52 Subgrade — — 9.3 8.4–10.5 45 26–78 Roadbase 132 120–1 50 – — — — (Bloc~9-16) 8 tirnpacted subgrade 155 130–180 6.9 5.6– 9.0 >72 > 35–> 100 Subgrade — — 4.9 3.2– 7.9 58 23–96 Roadbase 134 120–145 – — — — Sub-base 133 125–140 4.8 3.9– 5.3 >85 39–> 100 5 4 Ftil 79 57-140 4.5 4.0– 5.1 >87 66–> 100 Fi~ 96 45–160 6.2 4.2– 7.3 >51 22–> 100 Subgrade — — 9.0 7.5–11.0 19 6-36 Roadbase 115 90–130 – — — — 6 12 Sub-base 124 90–’170 12.6 11.3-14.0 >46 16–> 100 Fti 211 120–320 6.9 3.7–10.9 .>41 12–> 79 Fti — — 6.7 4.4–8.4 >41 8–71 ,. TNM 4 In+itu CBR restits and moisture contents of tie stab~ed roadbase Site No. 1 2 3 4a&b 5 6 No. of tests 10 5 11 12 10 12 Mean 16.9 17.5 13.3 10.7 4.7 11.6 Moisture content (per rent) Standard detiation 1.3 , 3.4 3.2 2.0 0.8 1.1 Range 14.2–18.8 14.0–21.1 9.1–17.7 8.3–14.2 3.3– 5.8 9.8–13.9 In-situ CBR results (per writ) Mean 136 M results> 100 124 W resdts >100 M results> 100 N1 results> 100 Standard detiation 26.0 29.5 Range 80–170 67–160 ———..... Transient deflection values in the verge&de wheelpath at the time of mp~g Site No. Drection Mean transient deflection (mm x 10-2) Towards Eldoret 73 1“ Towards Nfiru 71 2 Slow lane 61 Towards Mombma 64 3 Towards Nairobi 89 Toward Mombasa 14 (Block4;-8) Towar& Nairobi 58 Towar& Mombma 36 (Blocb4:-16) Towar& Nairobi 34 Towar& kga-hga 13 5 Towar& Mombasa 14 Towarda Mombasa 52 6 Towards hnga-tinga 59 11 Tm~ 6 Rut depti meaauremenh at tie time of samphg Site No. I ~rection ] Towards Eldore* 1 I Towards NaW 2 I Sow he 3 4a&b Towards Mombasa Towards Nairobi Towards Mombma Towarda Ntiobi Towarda Mga-hnga 5 Towards Mombw Towarda Mombaaa 6 Towards kn~hnga Rut depti (mm) I Off-side Mean 7.5 9.1 1.8 4.3 2.7 6.5 7.2 0 0 3.0 4.5 I Range I Mean I Range 3–19 II 4.4 2–11 3–18 5.2 0–12 0–14 j 1.3 I O-8 0–19 2.5 o– 7 0–12 2.7 o–lo 2–21 5.1 0–13 O–23 6.0 O–23 — o — — o — o–lo 1.8 o– 4 0–15 2.0 o– 9 12 Tmm 7 Tensile test results of blocks taken from verge-side wheelpath No. of samples No. of Site No. ~rection that fractured Mean samples prior to testing tested @/~2) Towards Eldoret 1 1 9 0.069 Towards Nakuru 2 4 0.073 *f Slow lane — 6 0.096 Towards Mombasa 1 8 3 0.035 Towards Nairobi 2 8 0.054 Towards Mombasa 7 7 4a&b 0.054 Towards Nairobi 5 7 0.064 Towards Mombasa 6 6 5 0.032 Towards bnga-hnga 2 9 0.057 + BIOCkS taken in both verge ~d offside wheelpaths at one chainage Standard deviation @/~2) 0.031 0.021 kge I Rtimated cumulative traffic loading before samphg @/mm2) (equivalent standard Aes) = Site open to traffic for approximately 10 years 0.053 0.035 ~.188 Site open to traffic for approximately 14 years 0.009 I 0,023 q.050 1.OX1O6 0.014 0.029 0.020 0.012 0.021 0.039–0.074 I 3.OX 106 0.028–0.097 I 1.2X106 0.0434.093 I 4.3x 106 a Site open to traffic for approximately 4 years ., .,, .,,, ,., ,,, .,. . ,,. . “,. mmmm — Wmm % m o E Zo 00. 0.0 mgo m m 000 I 000 mmmo . mmm 14 TNW 8 (continued) Wage 1 ~ainage 2 ~inage 3 Gainage 4 Mean tenstie strength (N/mm2) No. of samples tested Mean tende strength (N/mrn2) No. of samples tested No. of samples tested No. of samples tested Site No. bcations of block Towards bnga-hg: between wheelpatha Towards Mombasa between wheelpaths 4 3 0.225 0.139 4 3 0,278 0.222 5 Towards Mombasa verge~ide Towards Mombasa between wheelpaths Towards hnga-bng between wheelpaths Towards bnga-hng verge-side 3 2 3 3 0.029 0.016 0.023 0.051 2 2 3 3 0.035 0.029 0.045 0.045 0 3 2 3 — 0.030 0.065 0.074 6 ,,.,,.,,,,,.,, ,, ,“ ,. .,, . Site No. 1 2 3 5 6 * Vsw = BW = Osw = T~~ 9 Ntm of samples that fractured prior to testing Number of samples hcation of blocb* successfully removed and tested Vsw 21 BW 24 VSWand OSW 10 BW 5 Vsw 23 BW 20 Vsw 28 BW 34 BW 26 Vsw 18 BW 20 . verge-sidewheelpath between wheelpaths offside wheelpath Number of samples that fractured prior to testing 3 — 3 6 12 6 8 6 16 Block 1 ~~ “erge-side wheelpath Block 2 J 1 Between wheelpaths Centre line of road —— —— Block 3 I I Blink 4 ) 1 Between wheelpaths Verge-side wheelpath,, POSITION OF BLOCKS AT A CHAINAGE (exupt for Sites 2 and 5) METHOD OF REMOVING SAMPLES FROM A BLOCK Fig. 1 POSITION OF BLOCKS AND METHOD OF CUTTING SAMPLES ng 0 “;/ ‘\ T \/ J / Stabilised / roadbase 0 / / A Fig. 2 SAMPLE AFTER REMOVAL FROM ROAD . Supponed in a rigid frame through a universal coupling . ——— --—— ———. plates” ~ Sample resin + Load applied through a universal coupling Fig. 4 END CA~ USED IN A DIRECT TENSION TEST Y I I I I I I I I I I I I I I I I ❑✼ \ (luao Jad) palsal Pue paAowaJ Alln4ssaaons saldwes 40 ON ❑ o o ● o ● o m o w o m o m 0. 0 4 m o ( ~wu/N) qlfiuaJls ai!sual waJ!a Plate 2 SAMPLES AFTER CUTTING (1907) DdOS36380 1,400 10/80 HPLtd So’ton G191S PRINTED IN ENGLAND ABSTRACT TENSILE AND COMPRESSIVE STRENGTH OF SOME STWILISED ROAD BASESIN KENA: CR Jones and HR Smith: Department of the Environment Department of Transport, TRRL Supplementary Report 623: Crotihome, 1980 (Transport and Road Rewarch Laboratory). This report describes the measurement of the direct tensfle and unconfined compressive strength of samples cut from stabfised roadbases in Kenya. The test methods used are described, and the strength of the samples k compared tith the performance of the roads. The report concludes that although the bases have lost tensfle strength in service, they have not suffered serious structural damage and tith routine maintenance these pavements should continue to perform satisfactotiy. ISSN 0305–1315 ABSTRACT TENSILE AND COMPRESSIVE STRENGTH OF SOME STABILISED ROAD BASESIN KE~A: CR Jones and HR Smith: Department of the Environment Department of Transport, TRRL Supplementary Report 623: Cro~home, 1980 (Transport and Road Research hboratory). This report describes the measurement of the direct tenafle and unconfined compressive strength of samples cut from stabtised roadbases in Kenya. The test methods used are described, and the strength of the samples is compared tith the performance of the roads. The report concludes that although the bases have lost tensfle strength in service, they have not suffered serious structud damage and tith routine maintenance these pavements shodd continue to perform satisfactorily. ISSN0305–1315