WO2011061383A1 - Lightweight self-compacting concrete with structural fibres for refurbishing building slabs - Google Patents

Abstract

Lightweight self-compacting concrete with structural fibres for refurbishing building slabs. The invention comprises a concrete produced on the basis of standard ingredient amounts, using conventional materials in conjunction with lightweight expanded-clay dry materials, fibres and chemical additives, a plasticizer, a superplasticizer and a cohesion promoter, the latter being a methyl cellulose powder. A material is obtained that has well-defined fresh-state and hardened-state properties. Run-out is of the order of 650 mm and reduction at 575 mm in the presence of the Japanese ring, and it is a homogeneous material with a satisfactory capacity to pass via obstacles. In the hardened state, the concrete has a density around 1600 kg/m³, with mechanical strength close to 20 MPa in terms of compression strength and 1.2 MPa in terms of tensile strength at 28 days. The method comprises using the resulting concrete to refurbish slabs, in which the structural component is the Catalan vault.

Description

 Light self-compacting concrete with structural fibers for rehabilitation of building slabs

Technical sector

 The present invention concerns a lightweight self-compacting concrete with fibers, referred to herein as HLACF, produced by a standard dosage, which contemplates the use of conventional materials associated with light aggregates of expanded clay, structural fibers and chemical additives (plasticizer, superplasticizer and cohesive ).

Prior art

 The application of conventional standard density concrete in building structures is common practice in the construction industry. Conventional steel bar reinforcement is used in most application cases. On the other hand, the introduction of fibers in concrete is a technique that has high acceptance, since it provides an adequate response to the structural needs present in many situations. Fibers incorporated in concrete are responsible for improving the energy absorption capacity of the material, as well as its ductility. Some studies show that the fracture energy of a conventional concrete can be raised 40 to 50 times in response to the introduction of steel fibers in the mix. The fibers act as a bridge between the cracks formed, giving residual tensile strength to the concrete.

 In the same way, low density concretes (light concrete) are increasingly being applied structurally. The possibility of reducing the concrete's own weight associated with the maintenance of mechanical strength allows reducing the loads applied to the foundations, resulting in technical and economic feasibility.

 However, conventional concrete and light concrete require considerable energy and labor for the implementation and finishing activities to be carried out. An alternative to these problems is the use of self-compacting concrete (HAC, or SCC), that is, very fluid, homogeneous and stable concrete, capable of

REPLACEMENT SHEET (Rule 26) warp by action of its own weight, filling all the formwork sectors without the need for internal or external vibration and with the ability to overcome obstacles (for example reinforcement reinforcements), since its use allows to reduce the workforce at launch and improve the quality of the finishing of the pieces. In addition, HACs contribute to noise reduction during commissioning, which allows concreting in places where there is sound control and is positive for workers' health.

 In general, a HAC must have high fluidity, resistance to segregation and ability to pass through obstacles (such as reinforcement bars). However, the incorporation of fibers in that type of concrete can affect the aforementioned ability or ability to pass the material through the obstacles, depending on the added content and the length of the fibers. Complications concerning the homogeneity of the material may also occur in the case of steel fibers. The high density of these fibers promotes segregation, and it is necessary to increase the cohesion of the mixture, which reduces fluidity. Likewise, the incorporation of light aggregates in HAC demands increased cohesion, since these materials tend to float due to their low density.

 In WO-A-2006/056205, WO-A-2007/009408, US-A- 2007/0163470, CN-A-101 139192 and FR-A-2919602 different applications using HACs are described.

 Although complications such as those mentioned above are observed, the technical literature is abundant in HAC references with the addition of fibers or light aggregates. However, the combination of the three materials is not commonly found and information regarding the properties of the material in the fresh and hardened state is insufficient.

 As an example, it should be noted that in the recent international congress SCC2008 held in Chicago (USA), of the numerous communications presented (128) only one of them affected this type of solution, Tasdemir et. to the. (2008) "Comparison of workabilitty and mechanical properties of normal and lightweight SCCs with and without steel fibers". This communication describes a HAC (SCC) using steel fibers and light stone-pumice aggregate.

REPLACEMENT SHEET (Rule 26) The present invention provides an alternative proposal for a HAC with the addition of fibers and light aggregates that achieves better performance with respect to the HAC concrete described in the aforementioned communication by Tasdemir et. to the.

Explanation of the invention.

 It seems necessary to offer an alternative to the state of the art that allows to obtain a light HAC with fibers, that is to say an HLACF, which allows structural application of a low density material and can be launched in the most diverse places, even those that do not allow vibration of concrete.

 To this end, the present invention provides, in a first aspect, a concrete that meets the performance required for structural application, in particular for the rehabilitation of building slabs, associated with a low density. Likewise, the behavior in the fresh state is of high fluidity and workability, being in the range of self-compacting concrete.

According to the invention, a lightweight self-compacting concrete with fibers is proposed, of the type that includes natural aggregates, light aggregates and fibers, characterized in that said light aggregates are of expanded clay and have been dosed so as to provide a low density (from 1,400 to 1,800 kg / m ³ ) associated with the possibility of pumping the mixture, the fibers are structural fibers (steel or polyester) and at least one plasticizing chemical additive, a calcareous filler and a cohesive methylcellulose additive is used.

In order to achieve the required benefits, a water / cement ratio of around 0.45, cement consumption between 425 and 475 kg / m ³ and a total of fines between 550 and 650 kg / m ^{3 have been used} . The natural aggregates used are from crushing and consist of a 0-4 mm sand and a 4-10 mm aggregate. Light aggregates are made of expanded clay and have been used in two sizes and densities. The light aggregate 6-16 mm has density 325 ± 50 kg / m ³ and the light aggregate 3-10 mm has density 550 ± 50 kg / m ³ . The granular skeleton has been dosed so as to provide low density associated with the possibility of pumping the mixture. The addition of filler or calcareous filler and plasticizing, superplasticizing and cohesive chemical additives is

REPLACEMENT SHEET (Rule 26) absolutely essential to obtain the proposed concrete. As a cohesive agent, a methylcellulose powder is used, which allows to achieve a synergy between the components of the mixture although they have different densities. Finally, structural fibers (steel or polyester) of 30 mm in length and 0.5 mm in diameter have been used, around 0.4%, by volume.

 The combined use of natural aggregates of standard density and light aggregates responds to the need to achieve some workability based on the granular skeleton, which in this case is better obtained with natural aggregates than with artificial sands from crushing artificial aggregates of larger size Light aggregates are left for the largest fraction of aggregates. Likewise, the reason for the incorporation of the filler is, on the one hand, to improve aspects of workability and, on the other hand, to influence the mechanical strength of concrete, acting as a fine material and improving the compactness of the cement matrix.

 The combined use of the additives, plasticizer and superplasticizer, aims to obtain high fluidity along with maintaining that fluidity over time. The cohesive additive is necessary, since obtaining cohesion by increasing the fine material present in the mixture implies an increase in the compactness of the paste and consequent elevation of the concrete's own weight. Thus, the use of the cohesive additive has been essential and has resulted in homogeneous, workable and low weight concrete. The buoyancy trend of light aggregate has been controlled and the fibers have also been distributed throughout the concrete.

 The pouring of the components in the mixer has been done manually and in reverse order to the size of the aggregate; starting with coarse aggregates, up to cement and filler (or load). The kneader has been set in motion for homogenization of dry materials. Next, the fibers have been added with the mixer in motion. The cohesive additive, which is a powder, is added with the kneader stopped, followed by movement for homogenization. Each time the kneader is promoted to homogenize the materials the movement is

REPLACEMENT SHEET (Rule 26) about 30 seconds Water is added with the mixer in motion and the mixture is approximately 1 minute. Two liters of water are separated for addition together to the plasticizer and superplasticizer additives. These are added at the end, having a mixture of 1 minute after the plasticizer is added and 4 minutes after the superplasticizer is added.

 The tests carried out in the experimental campaign for characterization of fresh concrete are: runoff (according to UNE 83361: 2007), runoff with the Japanese ring (according to UNE 83362: 2007), occluded air (according to UNE-EN 12350-2: 2006 ) and density (according to UNE-EN 12350-6: 2006). The tests in the fresh state respond to the need to verify if the concrete produced is really self-compacting. In addition, they allow checking the homogeneity of the material through the existence of exudation and / or segregation of the mixture.

 In the hardened state, the tests proposed for mechanical characterization are: compressive strength (according to UNE 12390-3: 2003), tensile strength - Barcelona test (according to PrUNE 83515: 2007) and density (according to UNE-EN 12390-7: 2001). The tests carried out in the hardened state are intended to characterize the mechanical properties of the concrete in order to verify whether they are compatible with the required structural specifications of the material.

 The results obtained are around 650 mm of runoff. In the presence of the Japanese ring that value falls to 575 mm, so that the difference in concrete heights inside and outside the ring is 5 mm, which indicates homogeneity and ability to pass through the ring bars.

 In the following, various figures are presented that illustrate the behavior of concrete. Figures 1 and 2 show the appearance of fresh concrete in the runoff and runoff tests with the Japanese ring. The runoff test performed with the inverted Abrams cone has shown that the concrete remains homogeneous when passing through restrictions, as shown in Figure 3.

REPLACEMENT SHEET (Rule 26) On the other hand, Figures 4 and 5 want to reflect, on the one hand, the viability of the pumping, both horizontally and vertically and, on the other hand, the appearance of the concrete pumped at the end of the path. Description of some embodiments including pumping and application

With reference to figures 1 and 2, it has been verified that the fresh density is around 1380 kg / m ³ and the percentage of occluded air close to 8.5%.

On the other hand in the hardened state, the density of the material is increased, as a result of the hydration reactions of the cement and consequent increase in the compactness of the matrix. The value found for the proposed material is between 1,400 and 1,800 kg / m ³ . The mechanical resistances observed are around 20 MPa of compressive strength and 1.2 MPa of tensile strength, at 28 days.

 The experiments carried out on the occasion of the industrial verification of the HLACF according to the present invention, are supported by the experimental campaign carried out previously, in which the optimum dosage has been established by laboratory tests. The objective of the industrial contrast was to validate the results obtained in real-scale laboratory. This culminated in an HLACF pumping test conducted on July 28, 2009, at the PROMSA prepared concrete plant in La Garriga.

 The initiative to seek to carry out pumping tests for the HLACF is important because the commissioning is a condition regarding the application of said concrete in the rehabilitation of real structures. The results obtained in the laboratory, although they are very satisfactory, usually present changes, small or more significant, when produced on a large scale, at an industrial level. This can be the result of different factors, such as the storage conditions of the materials, the way they are poured into the mixer or concrete mixer truck, or the type / power of the equipment used to mix the materials. The fact that it is necessary to pump the concrete is also a condition of great influence especially to the concretes that carry light aggregates, since these aggregates are very porous and

REPLACEMENT SHEET (Rule 26) they must resist the pressure imposed by the pumping equipment well and not absorb excessive water.

The materials used in the pumping test performed have been the same as those used in previous laboratory HLACF experiments. However, the way of storage and dumping of those in the concrete mixer truck is different. As it is the production of a high volume of concrete (3 m ³ ), the discharge has been automated in the plant.

The starting dosage of the HLACF used is presented in Table 1. However, due to the characteristics of the concrete in the fresh state, it has been necessary to increase water consumption by 15 kg / m ³ , resulting in a final value of 215 kg / m ³ . The range where industrial solutions can be moved is also presented in the aforementioned table 1.

Table 1 - Starting dosage

 Dosage Dosage

 materials

(kg / m ³ ) (kg / m ³ )

 Cement 450 425-475

 Calcareous filler 100 75-125

 Arena 0-4 500 450-550

 Arid 4-10 80 70-90

 Light arid 3-10 85 70-100

 Light arid 6-16 85 70-100

 Plasticizer 2.7 2.5-3.0

 Superplasticizer 8.73 8.25-9.25

 Adhesive paste 0.85 0.75-1.00

 Fibers 6 5-7

 Water 200 190-225

 Total 1518 - The order and the way of pouring the materials in the concrete mixer truck are shown in Table 2. As can be seen, light aggregates have been poured manually, using a light crane. In industrial exploitation the aggregates will be in silos and will be incorporated into a concrete mixer by means of a conveyor belt.

REPLACEMENT SHEET (Rule 26) Table 2 - Order and form of pouring of materials in the concrete mixer truck

Materials Pouring form

 Light arid Manual, dry pouring

Natural aggregates, fibers, filler

 From the chalky conveyor belt and cohesive additive

 From the central silos

Cement

 dosing machine

 Urban water network and water part of

Water

 recycling (process performed at the plant)

Additives plasticizer and From the silos of the central superplasticizer dosing

In this contrast, several characterization tests have been carried out in the fresh and hardened state. In the fresh state they have been runoff (UNE 83361: 2007), runoff with the Japanese ring (UNE 83362: 2007), occluded air (UNE-EN 12350-2: 2006) and density (UNE-EN 12350-6: 2006), while in a hardened state: compressive strength of specimens (UNE 12390-3: 2003) and tensile strength - Brazilian test (UNE 83306: 1985).

Results

After the concrete has been kneaded, the runoff test has been carried out, which has indicated the need to adjust the dosage, so the water consumption has been increased by 15 liters, as previously stated. The results in the fresh state are presented in Table 3 and correspond to the samples taken before and after pumping. It shows that the results obtained show a self-compacting concrete and the density is in the established range (1,400 to 1,800 kg / m ³ ).

 The pumping has been done in both directions: horizontal and vertical. It is important to highlight that before pumping the concrete presented a slight excess of water and the beginning of exudation, although this problem was solved, thanks to the pressure imposed by the pump leading to water penetration (and also a little paste) in the pores of the light aggregate. Thus, the concrete becomes good, homogeneous and is suitable for the application.

REPLACEMENT SHEET (Rule 26) Table 3 - Results in fresh state

Figures 4 and 5 show the pumping in the horizontal and vertical directions, respectively. It is observed that the concrete pumped in both directions has a good appearance and homogeneity. No exudation is visualized and light aggregates are equally dispersed in the mixture, with no segregation or buoyancy of those aggregates. In addition, the concrete flows and drains by unique influence of its own weight, so that the self-compaction of the material is observed.

 The results in the hardened state are presented in Table 4. It can be seen that the resistance at 28 days is somewhat lower than the 20 MPa initially obtained in the laboratory. This may be due to the increase in water consumption and, consequently, the water / cement ratio (from 0.45 to 0.48). However, this decrease in resistance does not limit the application of HLACF in rehabilitation of unidirectional floors, where the

REPLACEMENT SHEET (Rule 26) Structural compression aspect is not so relevant. It is important to highlight that the weather (sun and hot weather) can influence the dosage, a circumstance that occurred on the day of the contrast, so it may be necessary to increase water consumption.

Table 4 - Results in hardened state

 Results

 Resistance tests (MPa) Before after pumping pumping

 3 days 16.3 14.7

 Resistance to

 7 days 14.9 14.8 compression

 28 days 17.8 17, 1

 Tensile strength 7 days 1, 80 1, 49

From the observed results, it is concluded that the industrial implementation of the HLACF has been carried out successfully. The pumped concrete has characteristics in a fresh and hardened state that allow its application in the rehabilitation of floors. The high workability is verified keeping the concrete homogeneous after pumping, even, as is the case, using light aggregates in the dry condition. The heat that was on the day of production may have been responsible for increased water consumption, so that the compressive strength of concrete has decreased. However, this is not limiting to the application of concrete in the rehabilitation of floors.

 The concrete of this invention can find an application in the rehabilitation of floors where the structural element is the Catalan vault. The concrete will be applied in this case on the vaults, the filling material being between the ceramic vault and the upper floor. This is applied in that way since the concrete is designed to resist the mechanical stress to which it will be exposed.

 A person skilled in the art could introduce changes and modifications in the described embodiments without departing from the scope of the invention as defined in the appended claims.

REPLACEMENT SHEET (Rule 26)

Claims

Claims 1 .- Light self-compacting concrete with fibers, of the type that includes natural aggregates and light aggregates and fibers, characterized in that said light aggregates are of expanded clay and have been dosed so as to provide a low density (between 1,400 to 1. 800 kg / m ³ ) associated with the possibility of pumping the mixture, the fibers are structural fibers (steel or polyester) and at least one plasticizing chemical additive, a calcareous filler and a cohesive methylcellulose additive is used.  2. Concrete according to claim 1, characterized in that said cohesive methylcellulose additive is provided in powder form.  3. - Concrete according to claim 1, characterized in that a superplasticizer additive is also used.  4. - Concrete according to claim 3, wherein said chemical superplasticizer additive is chosen from a group comprising water reducers based on polycarboxylates (with consumption between 1, 8 and 2.1% on the weight of cement).  5. - Concrete according to claim 1, characterized in that said plasticizing chemical additive is chosen from a group comprising polyfunctional water reducers (with consumption between 0.5 and 0.7% on the weight of cement). 6. - Concrete according to claim 1, characterized in that said calcareous load is between 75 and 125 kg / m ³ .  7. - Concrete according to claim 1, characterized in that said structural fibers (steel or polyester) are approximately 30 mm in length and approximately 0.5 mm in diameter used in the environment of 0.4%, by volume of the total of concrete.  8. - Concrete according to claim 1, characterized in that it has: a water / cement ratio in the vicinity of 0.45; a cement consumption between 425 and 475 kg / m ^3, and a total of fines between 550 and 750 kg / m ³ , where the natural aggregates used are from crushing and consist of a 0-4 mm sand and a 4-10 mm aggregate. 9. - Concrete according to claim 1, characterized in that the light aggregates are of expanded clay and have been used in at least two different sizes and densities.  10. - Concrete according to claim 9, characterized in that said light aggregates comprise: a light aggregate 6-16 mm of density 325 ± 50 kg / m ^3, and a light aggregate 3-10 mm of density 550 ± 50kg / m ³ , the granular skeleton having been dosed so as to provide the said low density associated with possibility of pumping the mixture.  eleven . - Concrete according to any one of the preceding claims, characterized in that it presents self-compactability in the fresh state, with opening diameter in the runoff test of the order of 650 mm and reduction to 575 mm in the presence of the Japanese ring, with good passage capacity through obstacles 12. - Concrete according to claim 1, characterized in that it has a density in a hardened state in the surroundings of 1 600 kg / m ³ , with a mechanical resistance in the environment of 20 MPa of compressive strength and 1, 2 MPa of resistance to traction, at 28 days.