LTRC. Alternative Tests for Durability of Cement Stabilized Low Plasticity Soils. Presentation to Louisiana Engineering Conference.

Transcription

1 Alternative Tests for Durability of Cement Stabilized Low Plasticity Soils Presentation to Louisiana Engineering Conference LTRC February 27 Louisiana Transportation Research Center

2 Background o Portland cement has been effective in improving the engineering properties of a wide variety of soils, including granular materials, silts, and clays o Two important engineering properties Strength/stiffness 3 psi for 8.5 soil cement 15 psi for 12 cement-treated Lab test, TR 432 Durability AASHTO 135 or ASTM 559 DOTD Only for special soil types Follow AASHTO 135

3 Durability Test o Time consuming 12 wet dry cycles, 6 8 weeks o Specimen preparation is important to prevent premature failure Break down along the interface of compaction layers o Need for a quick and better method o Intrinsic correlation between the strength and durability

4 Strength vs. Durability (from Portland Cement Association)

5 Dielectric value Tube Suction Test by Saarenketo and Scullion Time (hour)

6 Tube Suction Test cont. o A capacitance probe measures the dielectric value (DV) of materials o Some typical dielectric values Air: 1; Soil solids: 3~5; water: 81 o Is only used to test aggregate base Sample with ability to absorb more free water will be less durable for their engineering properties

7 Tube Suction Test cont. Base Aggregate o Good: maximum DV less than 1 o Marginal: maximum DV ranging from 1 to 16 o Poor: maximum DV larger than 16 o Short test period: less than 2 weeks

8 Summary o The current durability test is too timeconsuming o Tube Suction and Strength Tests have the potential to be used to predict the durability of cement stabilized soils o There is a need to develop correlations that can be used to predict the durability of cement stabilized soils

9 Objectives of Research o Simultaneously compare, evaluate, and understand the three test procedures with respect to the durability prediction for cement stabilized soils o Establish tentative criteria for using DV or strength to predict/determine the durability of cement stabilized soils

10 Dry Density (kn/m 3 ) Soil Properties Soil Type Silt (%) Clay (%) LL (%) PI (%) Optimum Moisture Content (%) g dmax (kn/m 3 ) Soil Classification USCS/AASHTO Silty Clay CL/A-6(15) pcf Standard Proctor Curve Zero air void curve TS Samples w opt =18.5% dmax=16.4kn/m Moisture Content (%)

11 Planned Test Factorial Molding moisture content Cement content (%) Dry unit weight (kn/m 3 /pcf) Planned tests 15.5% / % 16.4/ % 16.4/ % 15.5/98.3 Wetting-drying durability Tube suction 7-day UCS

12 Tube Suction Test

13 Specimen Molding and Testing

14 DV Variation of dielectric value (DV) with elapsed time 4 36 Raw Soil days 4 days 6 days w=12.5% w=15.5% w=18.5% w=21.5% w=24.5% Time (hours)

15 Dielectric Value Dielectric Value Dielectric Value Dielectric Value % (a) w m =15.5% 32 (b) w m =18.5% % days 5 days 8 days 4 2 days 5 days 8 days Time (hour) Stabilized Soil 36 (c) w m =21.5% 32 (d) w m =24.5% 21.5% 24.5% Time (hour) Time (hour) Legend: w m = molding water content 2.5% cement 4.5% cement 6.5% cement 8.5% cement 1.5% cement 12.5% cement Time (hour)

16 Dielectric Value Dielectric Value Dielectric Value Dielectric Value Dielectric Value Dielectric Value Time (hour) (a) cement=2.5% (c) cement=6.5% w m =18.5% w m =21.5% w m =24.5% (b) cement=4.5% 2.5% 4.5% 2 days 6.5% 5 days 8 days Stabilized Soil 2 days Time (hour) (d) cement=8.5% 8.5% 5 days 8 days Time (hour) Time (hour) (e) cement=1.5% (f) cement=12.5% % % Time (hour) Time (hour) Legend: w m = molding water content w m =15.5%

17 Max DV Influence Factors on Max DV % moisture 18.5% moisture 21.5% moisture 24.5% moisture Cement, %

18 Observation o Both molding moisture content and cement content affect the specimen s ability to absorb free water o Increase of cement usage delayed moisture intrusion and reduced free moisture in cement stabilized soils

19 Max DV Influence Factors on Max DV Cont Water-Cement Ratio 12 pcf, average 96 pcf, average

20 TS UCS, psi Influence Factors on TS UCS % moisture 18.5% moisture 21.5% moisture 24.5% moisture Cement, %

21 TS UCS, psi Influence Factors on TS UCS cont pcf, average 96 pcf, average Water-Cement Ratio

22 TS UCS, psi TS UCS with Max DV pcf, average 96 pcf, average Max DV

23 Seven (7) Day UCS

24 7 Day UCS, psi Variation of Seven Day UCS pcf, average 97 pcf, average Water-Cement Ratio

25 UCS, psi Comparison of Seven Day UCS day UCS TS UCS Water-Cement Ratio

26 Durability Test

27 Soil Cement Loss, % Variation of Soil Cement Loss %, average 18.5%, average 21.5%, average 24.5%, average A-6, 7% Cement Content, %

28 Observation o Soil cement loss is well correlated with cement content, but its strength and Max DV is not o Soil cement loss is not a good indicator for the variation of strength and ability to absorb free water o Is soil cement loss the best indicator for the durability of cement stabilized soils?

29 Durability Prediction

30 Soil Cement Loss, % Durability Prediction from Max DV %, average 18.5%, average 21.5%, average 24.5%, average Max DV

31 Soil cement loss (%) Durability Prediction from Max DV cont testing data 95% low er 95% upper y =.1287x R 2 = Maximum DV * Water Cement Ratio

32 Water cement ratio Durability Prediction from Max DV cont Samples failing PCA soil-cement loss criterion Samples passing PCA soil-cement loss criterion Boundary curve: MDV*w/c=29.7 Boundary curve, Maximum DV

33 Soil Cement Loss, % Durability Prediction from 7 Day UCS Day UCS, psi 15.5%, average 18.5%, average 21.5%, average 24.5%, average

34 Soil cement loss (%) Durability Prediction from 7 Day UCS cont Testing data 95% low er 95% upper y = 1.892x R 2 = Water cement ratio/7-day UCS

35 Water cement ratio Durability Prediction from 7 Day UCS cont Samples failing PCA soil-cement loss criterion Samples passing PCA soil-cement loss criterion Boundary curve, +.5 Boundary curve: w/c=.27*ucs day UCS, psi

36 Conclusion o Good correlations exist among the maximum DV, 7-day UCS, and soilcement mass loss. o Therefore, the water susceptibility for cement stabilized soils can be evaluated and predicted by these methods Tube Suction 7-day UCS Durability test

37 Conclusion - cont. o The water-cement ratio of cementstabilized soil had a significant influence on the maximum DV and 7-day UCS o The dry unit weight of cementstabilized soil could cause variations in the maximum DV and 7-day UCS

38 Recommendation Since primarily CL material was used, additional soil types should be tested to improve these charts for future use in design and construction

39 Question?