Code of practice for manufacture and use of lime-pozzolana concrete blocks for paving
1982 Edition

Per the guidelines in Clause 4.1 Table 1, the suggested mass-based mix ratios for lime-pozzolana concrete blocks are as follows: For the LP20 lime-pozzolana mixture, use 1 part lime-pozzolana mixture, 1 part fine aggregate, 2 parts coarse aggregate (20 mm), and 11% water by mass. For LP40 mixture, proportions are 1 part lime-pozzolana mixture, 2 parts fine aggregate, 4 parts coarse aggregate, and 10% water. When lime and pozzolana are used separately with lime reactivity at 40 kgf/cm², the ratio is 1 lime, 2 pozzolana, 3 fine aggregate, 6 coarse aggregate, and 11% water. For 80 kgf/cm² lime reactivity, use 1 lime, 2 pozzolana, 6 fine aggregate, 12 coarse aggregate, and 10% water. These ratios ensure strength and durability of the paving blocks.

According to the standard, lime-pozzolana mixtures must conform to IS 4098:1982. Lime used should comply with IS 712:1984, which specifies building lime requirements. Pozzolanic materials like fly ash must fulfill the requirements set by IS 3812, and burnt clay pozzolana should meet IS 1489 or related specifications. Aggregates must be in accordance with IS 383 for suitability in concrete production. The mixing process involves adding part of the water initially, then coarse aggregate, lime, and pozzolana or their mixture, followed by the remaining water with thorough mixing for at least two minutes to ensure homogeneity.

To ensure the blocks develop adequate strength, curing must be conducted immediately after molding by moving the blocks with their base plates to a sheltered area that protects them from direct sunlight, strong winds, and rain. Covering the blocks with polyethylene sheets is essential to preserve moisture. The initial curing period should last a minimum of 72 hours before the blocks are handled. Additionally, the water used should be clean and potable, free from harmful substances. These measures prevent premature drying and cracking, thereby supporting proper hydration and strength development.

The blocks should measure 300 mm by 300 mm in length and width, with a thickness of 100 mm. The layering consists of a 90 mm thick base layer made of lime-pozzolana concrete, topped by a 10 mm thick cement-sand wearing course. The mix proportions for the base layer vary depending on the lime-pozzolana grade but generally follow the ratios provided in Clause 4.1 Table 1, ensuring durability and appropriate mechanical strength for paving applications.

The standard specifies that the 90 mm thick lime-pozzolana concrete layer should be compacted using a pan-type surface vibrator, table vibrator, or by manual tamping in two successive layers to achieve uniform density. The 10 mm thick wearing course, composed of a cement-sand mortar mixture with a water-cement ratio around 0.5 to 0.55, should also be compacted using similar vibratory equipment or hand tamping. Adjustments in workability of the mix may be necessary depending on the compaction method used to ensure optimal block density and strength.