PU Injection Grouts
In the nineteenth century, a French civil engineer was deputed for managing and operating the harbour of Dieppe in France. He found to his dismay that the soil under the shallow foundation of the tide sluices built on gravelly material had critically eroded and the heavy undercurrents had endangered the safety of the harbour structures. He thought that he had to discover some innovative materials to surmount this perennial problem faced by the marine structures. The engineer was Charles Berigny who invented the first injection grout in 1802. He devised a new process of injecting a low viscous cementitious material by a pressure pump into the voids, fissures and crevice of the structures in order to reduce the permeability and increase the strength. This process was afterwards named as grouting. A few decades later in 1876, Thomas Hawksley injected grouts into rock fissures beneath the Tunstall dam and subsequently in 1896, a horde of British engineers grouted the dams built on the Nile using cementitious grouts.
Injection grouting is a process of filling the cracks, voids or honeycombs under pressure in concrete or masonry structural members for strengthening the damaged substrates. And the low viscous, flowable and non-shrink material that is injected unto fissures is called grout. There are different types of grouts which can be largely classified as cementitious or polymer grouts. This article will broadly cover the generic grouts and PU injection grouts in particular.
In order to strengthen the weak soils, dams, tunnels, and bridges, the cementitious grouts have been in larger use for almost nine decades. A cementitious grout is composed of a finely ground mixture of Portland cement, pumice, volcanic materials and dispersants. These ultrafine grouts which are injected into structures under pressure, traverse through the fissures and then harden into a solid mass. In order to minimize the shrinkage during cement hydration, suitable shrinkage compensating agents are incorporated in the grout formulations and these are popularly known as non-shrink grouts. Another variety of this kind, the gas-forming injection grout, works on a principle that the gas bubbles expand the grout to compensate shrinkage after application. These gas bubbles are generated on reaction of some ingredients like aluminium or carbon powder with the cement. Fibres such as polypropylene, steel or glass fibres are sometimes used along with cement grouts to provide improved flexural strength. In certain grouts, expansive additives are used to promote expansion at hydration. However, the use of cement grouts generally results in shrinkage and cracking at hardening and is not recommended for moving cracks in the concrete structures.