Grouts & grouting (Part-II)

Contd. from Part-I….

For mixing purpose, revolving type, tilting mixer of suitable capacity may be used. For preparing small quantity of grout, large mixer drum is not suitable as proper mixing won’t take place. Mixing needs to be done for a minimum period of 3 minutes & mixing location should be as near as possible to the location of grouting.Freshly mixed grout should be placed within 15 – 20 minutes of completion of mixing in order to maintain quality & the quantity to be mixed may be estimated accordingly.

Grouting operation should preferably be done from one direction only in order to avoid air getting trapped within.The grout needs to cover all shims to be retained and completely fill the annular spaces of all anchor bolts.

Once sufficiently set, the formwork is removed & excess grout, if any, is trimmed. Top surface of grout is float-finished smooth and sloping mildly outwards.

Curing for these grouts may commence immediately after a day of completion of grouting and continue for a week.

Regarding testing of cement-sand grouts prepared in-situ with OPC, cube compressive strength test is the usually adopted one even though there are few other tests as well. No of cubes to be taken depends on quantity of mix and is usually prescribed in relevant quality assurance documents. As an approx. rule, 4 cubes may be taken for first 5 bags of grout and additional 2 cubes for every additional 5 bags or part thereoff. Minimum 4 cubes must be taken even for small quantities. The freshly filled cube moulds are kept undisturbed for 24 hours after which the grout cubes are removed from moulds and submerged in water immediately. These are then taken out of water just prior to testing. Of the total number of cubes taken, half may be tested for 3 days strength and the remaining half for 7 days.

The size of the cube moulds is 70.6 mm as per IS:4031. Usually 3 & 7 day compressive tests are the most widely referred ones. However, often 1 & 28 day tests are also conducted. The minimum cube compressive strength for various periods are usually prescribed in relevant quality assurance documents. As a guideline, 3 & 7 days compressive strength for these grouts should not be less than 16 N/sq.mm & 22 N/sq.mm respectively.

Surface preparation prior to pouring grout involves more or less similar activities for all kinds of grouts. The top surface of foundation should be rendered rough in order to develope strong bond with fresh grout. The surface should be thoroughly scraped to free it from dirts, loose particles, oil, grease, mortar lumps etc. and must be wetted thoroughly for preferably a couple of days prior to commencing grouting. Just before pouring grout, excess water, if any, should be removed. Pockets, if any, may need to be vented to facilitate full penetration of grout.

Contd. in Part-III….