Bleeding of cement based grout
Bleeding of cement based grout is a complex problem. How it occurs and which basic mechanism causes and influences bleeding have been questions for discussion. Therefore the aim of the thesis is to illustrate what really happens with grout during bleeding and which factors influence it. In this way relevant measuring methods can be developed as well as the knowledge regarding how to interpret measuring results to joints in rock.
The bleeding tests show that there are two basic mechanisms which cause bleeding. They are sedimentation and consolidation. It also means that the bleeding process is influenced by sample height. It was found that bleeding of coarse cement (ANL) was mainly a result of sedimentation of the grout. Experiment with fine cement (INJ30; d95<30 µm) shows that the consolidation part of bleeding was larger.
The study shows that the bleeding process for a low sample height (10 mm) occurs fast. Extrapolation of experiment results and theoretical analysis shows that bleeding in a joint happens very fast and takes place during grouting itself. It means that results measured by standard methods can not be applied straight off for joints in rock.
Theoretically bleeding occurs relatively slowly in vertical or inclined joints due to increased height. Bleeding will be resisted by arching and hardening. Reasonably, very little bleeding will take place.
Filtration of cement based grout
How far grout penetrates into a joint is not just influenced by the rheology of the grout like viscosity and shear strength, but also by the tendency of the grout to get stuck which means to build a plug. Factors which influence the building of a plug are properties of the grout, geometry of the joints including rawness of the joints and proceeding of the grouting.
Today there are many different ways to measure filtration of a grout or the building of a plug. The different methods give different results and thus the importance of the influence of different factors is interpreted differently.
The experiments in this thesis are done in a 100 mm long, 50 mm wide aperture with 1 mm width. Thereafter the width of the aperture decreases to 0.02 – 0.3 mm over a 10 mm long distance.
The results of the experiments in this thesis, measured by own method, show that the best penetration ability with respect to filtration has a grout based on relatively fine-graded cement (INJ30; d95<30 µm).The penetrability of the grout based on more graded cement decreases because of flocculation. In total tens measurements have been done. The measurements confirm others’ experiments which show that the concentration of fine-graded particles (< 4 µm) has a large influence on flocculation and with that the building of larger grains.
It is important to remind that the mixing of grout has been done by a laboratory mixer, which is not a mixer of colloidal type. This issue has to be further tested.
The research shows that filtration of grout is also influenced by grain size of cement and the water cement ratio. The filtration test carried out by own measuring method with varying pressure showed a better penetrability for a larger pressure. It influenced both arching and erosion of the accumulated particles.
Stockholm: KTH , 2007. , 177 p.