Injection of Resins :: Waterproofing  :: Consolidation

Injection of Resins

Introduction

The injection of “concrete milk” is almost always used as a more economic alternative to preventive consolidating or stabilizing works. In many cases, nevertheless, this kind of solution proves being little useful or useless. When the work is to be executed below the ground level, or for consolidation and waterproofing works, it is quite often necessary employing different technologies and materials, having peculiar properties

Among the different kinds of synthetic materials we may put in evidence:

Bi-component polyurethane (PUR) resins, composed by one part of MDI (Isocyanides) and one of “Polyoils”. The mixture of these two components in a correct proportion allows the constitution of a final, hardened PUR resin. The properties of the different resins, both in liquid or solid condition, may dramatically vary according to the different kinds of existing formulation. It is possible to affirm, in general, that one of the main features of these resins is their possibility of increasing their volume in the presence of water or humidity. They may be employed whenever you wish obtaining a permanent waterproofing and an elastic adhesiveness spite of the existing conditions of possible movement or vibrations (high elasticity and energy absorption).

Mono-component PUR resins , formed by one only polymer, have as a main catalyst the presence of water or humidity. A reaction accelerator is frequently added to the product, with the aim of piloting its hardening speed, according to the working situation. Such a material may be used for pre-waterproofing works (open cell, temporary waterproofing) and mainly when injecting to consolidate sandy granular grounds.

The Silicate resins, unlike the bi-component PUR, instead of a Polyoils mixture have an inorganic silicate modified in water solution, allowing the material achieving high adhesiveness qualities in the different substrates and, according even more to the kind of formulation, having a higher or lower increase of volume or related flexibility.  Silicate resins are specially used to consolidate rocks or ground in case of excavation because, once hardened, they behave like concrete mixtures.

Meta-acrylic resins, composed of three main components and dissolved into water, show a very low viscosity and are generally used to consolidate very fine sandy grounds or for the waterproofing of water veins with capillary concrete cracks where other materials are not able to penetrate, due to their viscosity.

These three kinds of PUR resins (mono-, bi-components and silicate) may present a more or less evident increase of volume due to internal factors (type of formulation) or external causes (presence or absence of humidity). According to this feature, the final product develops a higher or smaller cell structure, as a consequence of the kind of resin, which was mixed, of the working temperature, of the reaction speed, etc.

If the expansion of the resins is contrasted, (e.g. because the crack is very thin), the strength of the volume increase would cause an auto-injection process, especially within cracks in medium-granular structures, thus creating an “influence zone” (or “injection cone”) having a larger volume then actually injected.

In each intervention, as shown below, the factor of volumetric increase is regarded to as “free” expansion without contrast. The mechanical resistance of the finally resulting product is inversely proportional to the fee expansion factor, i.e. the final density, as shown below.

Reaction time (pot-life) is generally very short. For this reason, in order to guarantee a correct mixture, components A and B are to be pumped separately, by means of specific dosing pumps, fitted with manometers, no-return valve and pressure controllers, to allow the circulation of the components in a sealed circuit.

The pumps are supposed to forward the resin components, in the pre-determined proportion, until the final lance, where a static mixer treats them before the direct injection into the structure to be treated. This procedure also guarantees a reduction of ecological impact, as far as the resin and its reaction catalysts come in contacts with the environment when they are perfectly dosed and mixed. This reduces to the minimum level the transfer of possible organic components to the environment.

The mixture of resins is pumped to the injection point into the ground by means of a lance, i.e. a tube connected to a packer, fitted with a non-return valve, avoiding the reflux of injected material along the external wall of the tube itself, allowing at the same time to carry out the injection under pressure. The packer may be fitted at the beginning, at the end or in the middle of the hole. The choice may vary and depends from the kind of injection to be executed, the feature of the ground to be treated. The diameter of the hole may vary as well, mainly depending from the working conditions and the kind of tubes used (single, multiple, etc.)