Effect of individual components on characteristics of cement composites with recyclate

Transcription

1 Effect of individual components on characteristics of cement composites with recyclate VLADIMIRA VYTLACILOVA Department of Concrete and Masonry Structures Faculty of Civil Engineering Czech Technical University in Prague Thákurova 7, Prague 6 CZECH REPUBLIC vladimira.vytlacilova@fsv.cvut.cz, Abstract: - This article deals with the exploitation of construction and demolition waste of mineral origin for the production of new concrete. The exploitation of recycled and recyclable materials for new construction is an important aspect of sustainable construction which should become a priority in the design and choice of building materials. With depleting natural resources new possibilities must be sought for the substitution of natural aggregates, where, thanks to its properties, brick or concrete recyclate represents a suitable alternative solution. By adding polymer fibres to concrete mixes fibre concrete is produced a tough composite offering by its properties a new application potential in structures. The article presents findings from a study and analysis of the results of an experimental programme focused on the production of concrete and fibre concrete in which natural aggregates have been substituted with brick or concrete recyclate. The research results are analyzed to monitor the effect of individual components on the properties of tested composites. Key-Words: - Construction and demolition waste; Recycling; Recycled aggregate; Structural concrete; Composite material; Fibres 1 Introduction Rapidly depleting deposits of non-renewable natural resources, high energy demands necessary for their extraction, negative effects on the environment during their extraction, processing and subsequent exploitation, all these persist to be one of the most serious problems of our time. A related phenomenon are growing volumes of piling up waste of various origin, and, in this respect, the building industry is one of the largest consumers of raw materials and energies (building industry consumes about 40% of energy and creates ca 40% of the total amount of man-generated waste). A potential solution to these problems is the exploitation of recycled materials. One of the friendliest ways of managing the volumes of piling up waste which does not impose a very high burden on the environment is the exploitation of recycled and recyclable materials (Fig.1). Construction& Demolition Waste Recycling Reprocessing Reuse Relocation Fig. 1 The four scenarios for materials use in the built environment In its wider context, recycling represents new material utilization for a different purpose and a system than the one in which it had originated and for which it is no longer usable. The scope of potential reuse of raw materials into new products is very wide and we may say that having mastered the waste processing technology, up to a 100% return rate of used material into new production may theoretically be achieved. Concrete belongs to the most used building materials worldwide, and, therefore, the effect of concrete structures on the environment, with a view to the volumes of its production, is very significant. In this respect, concrete construction offers numerous possibilities of solutions related to today so highly discussed sustainable development. The goal of the presented article is to sum up the findings and results of experimental research focused on monitoring the properties of cement composites with significant proportions of recycled aggregates. The research included the verification of achievable characteristics of a composite in which natural aggregates had been replaced with brick or concrete recyclate. The obtained results were subsequently compared with the results presented by other ISBN:

2 research workplaces. The analysis was to verify the effect of individual components on the characteristics of resulting concrete. 2 Current recycling rate within EU and Czech Republic In 2005, the European Union (EU) formulated a vision of the EU as a recycling community. The objective of this vision was to achieve construction with a lower exploitation rate of natural materials, energies and a lower production of greenhouse gas emissions, less polluting emissions into soil, water and the air. Pursuant to Directive No. 2008/98/EC on waste, the recycling rate of construction and demolition waste (CDW) (without soil and stone) in EU countries should reach 70% by The production of recycled aggregates from CDW (Construction&Demolition Waste) in individual EU countries ranges around 5-15% of the natural building aggregate production. Data on total CDW recycling in 18 EU countries files The European Environment Agency. Their data show that the overall recycling level in individual countries considerably varies. Total recycling rates in general is quite reasonable (>50%) for 11 countries. Five countries have very high recycling percentages (> 70%), six countries have recycling rates between 50% and 70% and seven countries below 50% [1]. The current recycling rate in the Czech Republic is still way behind the urgency of this problem. Like in the other EU countries, CDW in our country also accounts for one quarter to one third of all waste production by weight. It is clear that the main volume is brick and concrete debris (Table 1) [Source: ARSM]. Table 1 CDW processed in recycling line in CR (The amount in thousand of tones) Recycling Year waste Masonry Concrete Asphalt Mixed waste Aggregates Spoil Construction and demolition waste Large volumes of materials consumed in construction also represent a great potential for the exploitation of recyclable materials from other sectors than the building industry. Construction and demolition waste arising in the production of building materials and construction activity covers a whole range of materials which, thanks to their typical properties, offer a wide scale of exploitation. These are mineral inorganic materials of mostly inert nature without hazardous properties in which no significant physical, chemical or biological transformations occur. The exploitation of mineral construction wastes has been shifting from reclamation and landscaping projects towards real recycling and subsequent exploitation of recycled materials into new products. The recycling process of concrete applies two types of recycling [3]: Recycling of downward type (down-cycling) Recycling of upward type (up-cycling) Recycling of CDW is a relatively simple process which is based on quality recycled sorting. Recyclate containing solely crushed concrete (at least by 90%) coming from building structures and structural members is called concrete recyclate. Very useful recyclate is obtained from demolitions of concrete roads and motorways or railway sleepers where high-quality concretes of higher strength classes had been used. If appropriately segregated, very high-quality material may be obtained which is in great demand on the part of building companies and is presently increasingly more used as filler into concretes with lower demands for strength. Open literature commonly recommends the application of ca 30% of recyclate as substitution for natural aggregates. Many studies have proved that with this amount the properties of concrete are maintained at an acceptable quality level, often without any significant differences against concrete with natural aggregates. It is commonly used as filler into bitumen mixes, backfills or as base material in road construction. Among its main disadvantages there is heterogeneity of materials, lower volume density of recyclate grains ( kg/m 3 ), higher moisture absorption (5-10%, in fine grading of 0/4 mm over 10%) and poor durability of fines (they contains a large proportion of cement stone). The formerly unused due to its insufficient properties 0/4 mm grading has now found its application in the production of cement. ISBN:

3 4 Use of recyclate in concrete One of new possibilities is the exploitation of masonry recyclate in the production of structural fibre reinforced concrete [3-7]. Fibres help to strengthen the structure of concrete with masonry recyclate enhancing, above all, the tensile characteristics of the resulting fibre concrete thus extending its application potential. High demands for the composite s full structure do not apply for selected applications. These facts relatively well define reasonable precision of the grain composition of recycled components in wide grain-size fractions as well as the application area for these composites. In practice, this great advantage will mean that degraded parts of a structure (manifested by cracking along the whole cross-section) will still hold together. This, in fact, is also manifested by falling branches of pseudo-working diagrams of fibre concretes with masonry or concrete recyclate [3]. This composite may be suitable mainly for newly built road and water management earth structures with a limited appearance and occurrence of cracks (e.g. consolidation of slopes, embankments, dam crest trenches) and also for road pavement layers, layers of industrial floors and multipurpose halls, for the construction of diverse utility services, parking places, sports grounds etc. [7]. 6 Mix design The experimental programme produced a wide scope of results [3-7] pointing out the achievable properties and behaviour of fibre concretes with recyclates - masonry or concrete debris. The formulas differed by the dosage of mixing water preserving the required consistency. The amount of cement was dosed in a range of kg per 1m 3 of concrete. Specimens with cement amounts lower than 240 kg/m 3 already contained a large volume of pores and showed insufficient homogeneity of the composite. All tested formulas were produced with Portland fly-ash cement CEM II/B V 32,5R. Optimal amount of cement was 260 kg/m 3. Specimens were made with polypropylene fibres suitable for their strength and corrosion resistance. Their amounts in the formulas were specified on the basis of preceding experimental tests with fibres used in 0,5-1% of the total volume to prove their more significant effect in the concrete structure with recyclates at still reasonable economic efficiency rates. The fibres are ca 50 mm in length and their tensile strength is ~ 700 MPa. The fibres tested in this project came from the manufacturer emzet (Forta Ferro). The water/cement ratio was in the range of and was modified so that the required workability would be achieved. 5 Experimental programme The experimental programme dealt with the verification of selected material characteristics of the composite relevant for presumed applications. To obtain a wide scope of results, more potential alternative versions of mixes with different amounts of binder, different water/cement ratios and different types and amounts of fibres were produced to assess achievable characteristics of the composite. The experiments included the production and subsequent testing of concrete in which aggregates had been fully substituted by masonry or concrete recyclates. The key parts of the fibre concrete mix are the basic components: aggregates recyclate, cement, water and fibres. Their specific ratios and the properties of individual components principally affect the resulting behaviour of fresh fibre concrete and the characteristics of the final product. Due to the demand for minimizing the price of the composite, the formulas were modified so that no extra admixtures or additives improving the characteristics of concretes would be necessary while preserving sufficient workability. Fig. 2 Fibre reinforced concrete with full replacement of recycled masonry aggregate 7 Knowledge of experimental research In terms of this research were used standard test methods for determination of mechanical-physical properties as initial bulk densities, compressive strengths, flexural strengths and tensile-splitting strengths ISBN:

4 The resulting strength of concretes made by substituting natural aggregates with recyclates is mainly affected by the cement dosage, the water/cement ratio and the properties of used recyclate. The strengths of concretes produced with complete substitution of natural aggregates by recyclates were lower than in the case of concretes with natural aggregates, which is given by the nature of the inert component, i.e. crushed bricks, masonry or concrete. This fact was mainly manifested in specimens without fibres where the difference in strength accounted for up to 30%. In the case of fibre concretes the difference in strengths was on average 10%. The results point out a slight difference in monitored strengths in using pure brick or impure crushed masonry. The difference between concrete and masonry recyclate is interesting. The strengths of specimens with concrete recyclate were lower than the strengths of specimens with concrete recyclate, which testifies to a great effect of the quality of input material recyclate. The effect of the aggregate type was also manifested on the volume density of specimens. The volume density of the composite with masonry recyclate is on average 1963 kg/m 3, while with concrete recyclate 2027 kg/m 3, whereas in concretes with natural aggregates the value of 2260 kg/m 3 was detected, which corresponds to the values quoted in literature. The determined volume density values of produced test specimens confirmed the fact that volume density of concretes with recycled aggregates is lower than that of concretes made with natural aggregates, which results from the nature of the inert material component. The expected presumption that the scattering of values would be greater for specimens with masonry recyclate than for common concretes and fibre concretes produced with natural aggregates was confirmed; this difference, however, was not very dramatic and may be considered satisfactory. This fact again corresponds to the nature of the used inert material. The specimens of a composite produced simultaneously with brick and waste natural aggregates and cement amounts of only 150kg/m 3 reached very low strength values, but may represent an interesting option in the case of undemanding requirements for concrete characteristics. The value of the cylinder strength f ck to cube strength f ck,cub ratio is roughly 0.8. In the case of fibre concrete the stated value is According to the results of the experimental programme the cylinder to cube strength ratio of fibre concrete with recyclates exceeds 0.9 (equalling 0.91 for specimens with masonry and 0.97 for specimens with concrete recyclate). It was confirmed that the characteristics of the composite may be significantly regulated by its composition and the weight ratio of components: by increasing the quantity of cement within the tested range strengths may be increased by more than 50%. Thus, cement quantities of over 400 kg/m 3 may result in achieving relatively high strengths of over 30 MPa. Compressive strengths of composites with masonry recyclate ranged from 12 up to 33 MPa, while transverse tensile strengths ranged from 1.82 up to 4.04 MPa and tensile bending strengths from 1.85 up to 6.05 MPa depending on the quantities of cement and the ratio of the other components. A more dramatic difference in the strength growth in relation to the quantity of cement was identified for specimens produced with natural aggregates. The effect of cement had also proved essential in experimental research projects presented in [8-11]. The set of obtained values also reflected the effect of the amount and type of fibres on the characteristics of tested composites, which unambiguously positively affected the tensile strength values. Load [kn] Average value - 0,5% Characteristic value - 0,5% Average value - 1,0% Characteristic value - 1,0% 0,0 1,0 2,0 3,0 4,0 5,0 Deflection [mm] Fig. 3 Average and characteristic resistance diagrams of specimens with 0,5 and 1,0% vol. fibres FORTA FERRO and masonry rubble In concretes with higher strengths, however, it was less prominent. We may state that the effect of fibres on the characteristics of the composite was manifested in the same respect as in concretes with natural aggregates. The water/cement ratio of tested specimens was in a range of depending on specific conditions (absorption of recyclate) during their production. The effect of the water/cement ratio on strength characteristics cannot be objectively assessed for the ISBN:

5 reason of unknown initial moisture content and moisture absorption of the aggregates. Fig. 6 displays the strength to water/cement ratio relationship. Compressive strength [MPa] Cement kg/m3 Cement kg/m3 0,5 0,6 0,7 0,8 0,9 Water/cement ratio Fig. 4 Effect of water/cement ratio on compressive strength 7 Conclusion The efforts to widely exploit construction and demolition waste rank among top priority targets of many advanced countries which take care of saving natural resources and preserving the environment. With the ongoing depletion of natural resources, methods of reusing the piling up wastes of different origin must be sought. The method of reusing materials into production represents a great contribution to solving this issue despite the fact that recycling costs may be higher than the exploitation of primary resources. The completed experimental programme contributes to extending knowledge in using recyclates for the production of concrete and for setting the limits of achievable properties. Based on a large series of acquired experimental results on different characteristics of the tested material, it can be judged on the behaviour of this composite. The previous experimental program has proved that the properties of this concrete are sufficient enough to be used in ground structures as intended. Acknowledgement The contribution was elaborated with support of grant projects of Grant Agency of the Czech Republic No. 104/10/1128 and using the findings from project 1M0579 of Ministry of Education, Youth and Sport of the Czech Republic within the scope of CIDEAS. References: [1] Tojo, N., Fischer, Ch.; Europe as a Recycling Society, European Recycling Policies in relation to the actual recycling achieved, ETC/SCP working paper 2/2011, European Environment Agency. [2] Association for the development of recycling of construction materials in the Czech Republic, 5/2011. [3] Vytlacilova, V.; Fibre concrete with recycled aggregates as a full substitution of natural aggregates, Dissertation, Prague, [4] Vytlacilova, V., Vodicka, J., Hanzlova, H., Vyborny, J., Mechanical Physical Properties of Concretes with utilization of Crushed Bricks and Fibres, IASS ECS, Prague, [5] Vodicka, J.; Vyborny, J.; Hanzlova, H.; Vytlacilova, V.: Mixture Design of Fibre Concrete with Recycled Aggregate, 5 th Central European Congress on Concrete Engineering, Baden [6] Vytlacilova, V., Vodicka, J.; Properties of fiber reinforced concrete using recycled aggregates, Advances in Control, Chemical Engineering, Civil Engineering & Mechanical Engineering, Tenerife, 2010, pp [7] Vodicka, J.; Vyborny, J.; Hanzlova, H.; Vytlacilova, V.: Application of Fibre Concrete with Recycled Aggregate in Earth Structures, 5 th International conference Fibre concrete 2009 Technology, Designing, Application, Prague [8] Akash, R., Kumar, N. J., Sudhir, M.: Use of aggregates from recycled construction and demolition waste in concrete, Resources Conservation & Recycling, Vol. 50, No. 1, 2006, pp [9] Yang, J., Du, Q., Bao, Y.; Concrete with recycled aggregate and crushed clay bricks, Construction and Building Materials, Vol. 25, No. 4, 2010, pp [10] Hebhoub H., Aoun H., Belachia M., Houari H., Ghorbel E.; Use of waste marble aggregates in concrete, Construction and Building Materials, Vol. 25, No. 3, 2011, pp [11] Debieb, F., Courard, L., Kenai, S., Degeimbre, R. Mechanical and durability properties of concrete using contaminated recycled aggregates, Cement & Concrete Composites, Vol. 32, No. 6, 2010, pp ISBN: