The interpretation of the concrete mix design nomograph as shown in Appendix A is based on the inter-relationship between workability, water permeability, compressive strength against the water/binder ratio. For enhanced durability performance, it is recommended that water/binder ratio lower than 0.45 be considered in the mix proportions. If early strength is an important requirement, it is suggested that the TIA dosage should be around 5 % for high strength concrete and not greater than 10% for concrete of grades ranging from 25 to 45 MPa.

The effect of water/binder ratio on the 1-year compressive strength is shown in Figure 4. The plot was made with only two sets of values based on TIA concrete of grades 25 and 80. More tests on other grades of TIA concrete are necessary to verify the accuracy of the plot. The use of logarithmic scale on the y-axis is to achieve a curve quite close to a straight line so that the use of the concrete mix design nomograph is simplified.

The plot of water permeability against w/c ratio of the OPC control specimens is shown in Figure 5. The air-cured grade 80 OPC concrete achieved water permeability of around 1 pm/s. Similar TIA concrete specimens achieved lower water permeability of around 0.2 pm/s (Figure 3). The water permeability of the grade 25 OPC concrete was around 100 pm/s at the age of one year (Figure 5). Similarly cured TIA concrete exhibited lower water permeability of around 5 pm/s.

Figure 1: Effect of water/binder ratio on water permeability (28-day)

Figure 2:Effect of water/binder ratio on compressive strength (28-day)

Figure 3: Effect of water/binder ratio on water permeability (1-year)

Figure 4: Effect of water/binder ratio on compressive strength (1-year)

Figure 5: Effect of water/cement ratio on water permeability (1-year)

Figure 6: Effect of water/cement ratio on compressive strength (1-year)

A comparison between Figures 5 and 6 reveals that the effect of TIA on the compressive strength of air-cured concrete is rather small at the age of one year. The results indicated the possibility of producing controlled strength concrete with appropriate dosage of TIA as a partial cement replacement material in concrete. The plot of the compressive strength against the w/c ratio for OPC concrete of grades 25 and 80 is shown in Figure 6. The need for repeated tests and more accumulated data for other grades of concrete is reiterated. The relationship between the carbonation depth and parameters such as water permeability, w/c ratio and time is not shown in the concrete mix design nomograph because of very limited data on the carbonation depth. Based on the established theories cited by Lee, Y.L (10), it is postulated that the carbonation depth could be directly proportional to water permeability and the square root of time and w/c ratio (or inversely proportional to the square root of compressive strength).

1. A dual-test approach onto the standard 150 mm concrete test cube is proposed to be adopted with the use of the TIA concrete mix design nomograph. The non-destructive testing (NDT) of concrete cube for water permeability prior to the determination of compressive strength is a useful method of quality control in trial mix and during construction.

2. The development of the water permeability test system highlights the importance of design for durability and quality control of concrete structures throughout their designed life span. Its use on concrete test cube for the determination of water permeability prior to the standard test for compressive strength will provide useful information on concrete durability. The values of water permeability of a concrete structure can be monitored in-situ.

3. The appropriate use of TIA tends to enhance strength development and reduce water permeability of concrete if the cement replacement level is not more than 10 %. Water permeability of around 1 x 10 -13 m/s can be achieved for grade 80 concrete containing 5 % TIA. Concrete of reduced water permeability are suitable for products and structures subjected to constant water pressure such as the precast concrete piles and other concrete substructures.

4. The interpretation of the concrete mix design nomograph is based on the inter-relationship between workability, water permeability, compressive strength against the water/binder ratio. For enhanced durability performance, the water/binder ratio in the mix proportions is recommended to be lower than 0.45. If early strength is an important requirement, it is suggested that the TIA dosage should be around 5 % for high strength concrete and not greater than 10% for concrete of grades ranging from 25 to 45 MPa. However, it is important to note that the proposed TIA concrete mix design nomograph has certain limitations. It was based on limited data. The important relationship between workability and aggregate/cement ratio was not included in the nomograph which makes it somewhat incomplete. Further tests are therefore necessary.

5. The reduced water permeability of TIA concrete should be exploited through further in-depth research into high performance concrete subjected to constant water pressure. RHA which has a higher silica content is proposed to be processed together with TIA to produce a microsilica for use in concrete to achieve controlled water permeability. Concerted effort leading to quality enhancement of concrete through the exploitation of wastes in concrete for infrastructure development is a positive move towards improving the quality of life and conservation of the environment.

1. Lee, Y.L. (1997). "Non-Destructive Testing of Concrete Structures - Some Practical Aspects". Proceedings of Fifth International Conference on Concrete Engineering and Technology (CONCET '97), pp. 165-177 (presented on 6 May 1997).

2. Lee, Y.L., Siow, K. & Hussin, M.W. (1997). "Agricultural Fly Ash (AFA) - A Potential Alternative to Silica Fume for High Performance Concrete", ITTHO-PERKOM-IEM Seminar on Concrete Technology (rd-97) themed Research & Development for Competitive Advantage (presented on 2 October 1997).

3. Lee, Y.L., Bani, S., McNulty, G.J. & Hussin, M.W. (1997). "Acoustics Performance of AFA Concrete Paver Blocks", ITTHO-PERKOM-IEM Seminar on Concrete Technology (rd-97) themed Research & Development for Competitive Advantage (presented on 2 October, 1997).

4. Lee, Y.L. (1998). "Towards Achieving Quality Assured Maintenance - Malaysian Experience" Proceedings of 2nd International Conference on Planned Maintenance, Reliability and Quality, Oxford, England, pp.143-148.

5. Lee, Y.L., M.Warid Hussin & Ken Siow, (1999). "Experimental Production of Timber Industrial Ash (TIA) Cement Bricks: Malaysian Experience". Proceedings of International Conference on Infrastructure Regeneration and Rehabilitation. University of Sheffield, pp. 287-296.

6. Lee, Y.L., A. Aziz Abu Bakar., M. Warid Hussin, (1999). "Rice Husk Ash and Timber Industrial Ash Composite - Potential Materials for Low-Cost Housing", UTM Research Seminar, pp. 168-174 (presented on 4 February, 1999).

7. Lee, Y.L., Hussin, M.W. & Khoo, K.O. (1999). "Timber Industrial Ash Concrete". Proceedings of Sixth International Conference on Concrete Engineering and Technology (CONCET '99). The Institution of Engineers Malaysia, MARA Institute of Technology & University of Malaya, (presented on 30 June 1999).

8. Lee, Y.L., Khoo, K.O., Chong, S.S.F. & Hussin, M.W. (1999) "Strength Development and Water Permeability of High Strength TIA Concrete". Proceedings of International Congress on Creating with Concrete University of Dundee, pp. 175-181.

9. Lee, Y.L., A. Aziz Abu Bakar., M. Warid Hussin, Khoo, K.O., (2000). "TIA cement-lined pipes for waterworks", Proceedings of 3rd International Conference on Quality Reliability Maintenance, University of Oxford-UNECIA-I Mech E, (presented on 31st March, 2000).

10. Lee, Y.L. (1999). "Strength Development and Water Permeability of Timber Industrial Ash Concrete", PhD Thesis, UTM.

11. Cabrera, J.G. (1999) "Design and Production of High Performance Durable Concrete" Proceedings of International Conference on Infrastructure Regeneration and Rehabilitation, University of Sheffield, pp. 1-14.

12. Bob, C. (1999) "Durability of Concrete Structures and Specification" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & McCarthy) pp. 311- 318.

13. Ball, D. (1999) "New Ultra-Low Permeable Concrete" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & McCarthy) pp. 265- 278.

14. Hewlett, P.C. (1999) "The Role of Water in Determining Concrete Performance" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & McCarthy) pp. 63- 80.

15. Simon, M., Snyder, K. & Frohnsdorff, G. (1999) "Advances in Concrete Mixture Optimisation" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & McCarthy) pp. 21-32.

16. Somerville, G. (1999) "Whole Life Design for Durability and Sustainability. Where Are We Going and How Do We Get There?" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & McCarthy) pp. 1-19.

17. Corradi, M. & Khurana, R. (1999) "Durability…How Far Can It Be Extended With Admixtures" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & Dyer) pp. 475- 484.

18. Dewar, J.D. (1999) "Optimised Design Of Concrete And Its Components" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & Dyer) pp. 543 - 557.

19. Shimoda, T. & Yokoyama, S. (1999) "Eco-cement: A New Portland Cement To Solve Municipal And Industrial Waste Problems" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & Dyer) pp. 17 - 30.

20. Damtoft, J.S., Herfort, D. (1999) "Concrete Binders, Mineral Additions and Chemical Admixtures: State Of The Art and Challenges For The 21st Century" Proceedings of International Congress on Creating with Concrete University of Dundee, (ed. Dhir & Dyer) pp. 1-16.