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Cementbaserade injekteringsmedel.: Olika typer, cementreaktioner, bindetid och flytförmåga.
CBI - Cement- och betonginstitutet.
2003 (Swedish)Report (Refereed)
Abstract [sv]

A cement based injection grout is a slurry of particles. This slurry should be able to penetrate and fill cracks in the rock, where the slurry will stiffen resulting in a hard-ened product, which will stop water flow. For a good result you must be able to optimise and control both the penetration ability and stiffening. _x000D_ _x000D_ To get a background for how cements react chemically the work is divided in a theoretical and an experimental part, where the theoretical part takes into concid-eration the results from the experimental part. The injection cements are basically based on same clinker as ordinary Portland cements for construction purposes, but they are often more finely ground to be able to penetrate small cracks. As the hard-ening process is the same as for ordinary cements the theory for the ordinary ce-ments is considered. Hydration development, the use of chemical and mineral ad-mixtures and cement standards are briefly considered, as they form a theoretical background, which is useful when injection grouts are developed and optimised. _x000D_ _x000D_ Cement and other standards and regulations are intended for building purposes to give knowledge how different cements shall be used without giving any harmful consequences. An injection grout must not necessariliy follow these rules. Wrong cement in certain concrete combinations and in certain environments are swelling, thereby deteriorating the hardened concrete or cement product. The situation for a hardened injection grout is quite different, as it is locked in the rock and a swelling will result in tightening, which mostly is a benefit. This means that there are more degrees of freedom for injection grouts to mix different combinations of materials and to use different admixtures. It is, however, important to know what happens, so that the consequences can be considered properly in the actual case. For this reason both knowledge and testing are needed. _x000D_ _x000D_ An injection grout can be optimised both regarding penetration ability and stiff-ening/setting, but in most cases not both simultaneously. Often a compromise between different properties must be done. An injection grout suited for a specific situation is needed. The properties can be varied by using different cements, fine-ness, superplasticisers, chemical and mineral admixtures etc. _x000D_ _x000D_ In the experimental part of the work we have started from stable grouts for in-jection of cracks in rocks, which means that the grouts have such a cohesion that they do not separate. In some situations a rapid hardening is important and in other situations a slower hardening is allowed. Both slowly reacting and rapid hardening cements have been used together with different superplasticisers and in some cases mineral admixtures/binders, mainly to investigate the flowability and setting time. _x000D_ _x000D_ Generally rapid hardening is in conflict with good flowability. To get as stable grout as possible the w/b-ratio was mostly about 0,80, which will give a stable and strong hardened product. As the grout will be cooled in contact with the rock the experiments were performed at both room temperature and at 6-8°C, which is more relevant for the conditions in the Swedish rock. _x000D_ _x000D_ The purpose for the investigation was not primarily to achieve a specific grout, but to point out the controlling parameters and how they can be tested in the labo-ratory. _x000D_ _x000D_ Because of greater reaction surfaces a more finely ground cement reacts faster than a coarser cement and gives also a greater heat flow in a shorter time and a higher strength. With a finely ground cement it is more difficult to achieve a spe-cific flowability at a specific w/b-ratio, which means that the type and dosage of superplasticiser must be carefully optimised. If a grout with rapid hardening is wanted either an accelerator or a cement with an other composition is needed. _x000D_ _x000D_ The rapid reactions are mainly depending on the content of C3A, which reacts fastest of the cement clinker minerals. These cements are mainly used for house building purposes, where short setting times are wanted. Probably because of the rapid aluminate reactions the rapid hardening cements will get a worse flowability. A very finely ground cement with a moderate C3A-content of 7 % or more (the limit is not completely established), may give problems with false rapid setting. This is because the finely ground particles have changed the dissolution and reac-tion rates for the hydration processes. The result is an early rapid setting (false), which is not a result of the ordinary cement hydration. The false setting may how-ever be strong enough to stop water movements in the cracks. In the present inves-tigation the ordinary binding (from the ordinary cement reactions) could be delayed up to 40 hours. Also the superplasticisers give an other effect in the rapid hardening cements than in the slowly hardening cements. _x000D_ _x000D_ The false setting caused by aluminate/sulfate reactions can be controlled by a retarder e.g. citric acid and thereby the false setting can be utilised. This is the case for one of the investigated cements from Dyckerhoff. Its product Rock-U consists of a rapid hardening cement with a moderate C3A-content without gypsum. To control the setting a component called Compound B, which consists among other things of citric acid, is mixed with the cement. The more Compound B that is added the more the cement reactions are retarded, which gives a time dependent stiffening. Even though this stiffening is caused by a false setting, the ordinary reactions start later and by the time a hard and stable product is formed. _x000D_ _x000D_ If there is no demand on rapid setting the most secure (and cheapest) products are finely ground cements with a low C3A-content. Grinding a cement with a low C3A-content very finely, does not give any problems with too rapid hardening and also the flowability becomes good. Such a cement, which also was used in the in-vestigation, is the finely ground Swedish Degerhamn cement for civil engineering purposes. Different plasticisers affect the flowability and setting time differently. This is why the optimal plasticiser type and dosage must be achieved for every cement. A lower temperature (6-8)°C gives a stiffer grout and prolongs the setting time and also the difference between the different plasticisers is changed compared to the results at 20-25°C. This report shows a methodology to optimise grouts. _x000D_ _x000D_ Cements with a low C3A-content are slowly hardening and to accelerate the ce-ment reactions accelerators have been used. These can be used only to a certain limit, because too high dosages stiffen the grout markedly. The effect of using accelerators must be compared to the use of rapid hardening cements. _x000D_ _x000D_ Admixtures/binders like blast furnace slag, cristobalite (metastable quartz) and silica fume have also been tested. These can be used to dilute the cement or to give the grout a specified chemical composition. Also with these admixtures/binders good flowability is achieved, but with silica fume a gel is formed, which impair the penetration ability into small cracks. Finely ground blast furnace slag is the basic material in some injection grouts and can be mixed in different proportions with ordinary cements. The strength development, however, becomes slow. _x000D_ _x000D_ Altogether it can be said that good flowability was achieved with all the tested cements and mineral admixtures and that the slowly hardening cements can be accelerated to a certain degree, while the rapid hardening cements may give prob-lems with too early setting. A good flowability does not, however, guarantee that a good penetration in small cracks is achieved, since the filtration effect and gel for-mation may disturb the penetration. _x000D_ _x000D_

Place, publisher, year, edition, pages
Cement och Betong Institutet , 2003. , p. 104
Series
CBI rapport, ISSN 0346-8240 ; 2003:1
Keywords [sv]
injekteringsmedel, finmalda cement, långsamt härdande, snabbhärdande, flytförmåga, bindetid
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:ri:diva-2861OAI: oai:DiVA.org:ri-2861DiVA, id: diva2:960466
Note
269 Går att beställa: kontakta eva.lundgren@cbi.se (700 kopia/copy) "Cement based injection grouts. Different types, cement reactions, setting time and flowability"Available from: 2016-09-07 Created: 2016-09-07Bibliographically approved

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