FINLAND ADVANCES IN CONCRETE AND CEMENTITIOUS COMPOSITES AND APPLICATIONS TO CIVIL INFRASTRUCTURE

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Cameron Bridges
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1 FINLAND ADVANCES IN CONCRETE AND CEMENTITIOUS COMPOSITES AND APPLICATIONS TO CIVIL INFRASTRUCTURE Dr. Vesa Penttala Helsinki University of Technology Department of Civil and Environmental Engineering Espoo FINLAND ABSTRACT: This paper presents a summary of major advances in Finland in the concrete construction industry in the last decade ( ). The changes, which have taken place in the design of concrete structures, prefabricated concrete products, ready-mix concrete used at building sites, and ecological issues, are presented. Future trends, such as recycled new materials, self-compacting (self-consolidating) ultra-high-strength concretes, nonmaterial research, sensor technology, and smart buildings and materials, are briefly discussed. 1. INTRODUCTION Finland is situated in northern Europe and has a population of 5.2 million inhabitants. The construction industry uses about 10% of the annual income, and cement consumption is about 350 kg/inhabitant. The total value of construction industry in 2006 was 23.7 billion Euro ( ) [1 Euro = 1.36 US $). About 40% of concrete production was used in buildings and 60% in infrastructure building activities. New buildings and infrastructure comprise about 60% of the construction business, and the rest belongs to renovation and maintenance. Due to the cold climate during winters, about 30% of the produced concrete must possess some kind of a freeze-thaw durability property. Similarly, concrete production continues all year round, including during wintertime. 129

2 2. OVERVIEW OF THE LAST DECADE ( ) After the recession in the building industry in Finland during , construction activities quickly grew back to their normal pace. In the apartment and office building sector, precast unit production is much larger compared to other western European countries, which use ready-mix concrete at building sites in much larger amounts. In Finland, precast concrete unit production constitutes 60% of the concrete buildings and ready-mix concrete production the rest. Besides the harsh winter environment, this is mainly a consequence of the open building system developed in the 1970s, which has enabled the use of pretensioned hollow-core slabs in large quantities in apartment and office buildings and also in industry applications. It seems that even today the highly automized hollow-core slab production is quite competitive, and the basic five hole slab having a thickness of 265 mm (10.5 in) and a width of 1200 mm (4.75 in) has been diversified to consist of a large number of products having thicknesses from 150 to 500 mm (6 in to 20 in.). They can also be used in foundations and as wall units. The open building system has also made possible the introduction of prefabricated washroom units in apartment houses. Finnish construction companies perform concreting work during winter conditions at building sites. In southern Finland the normal minimum temperature for concreting is -15 o C (5 o F), and in northern Finland it is -20 o C (-4 o F). Heating or heat treatment is commonly performed by heating cables installed permanently inside horizontal and vertical forms. Preheated concrete is also commonly used, and sometimes infrared radiation heating is applied with steel moulds Design A product model data-concept has been developed and adopted in Finland during the last ten years (Figure 2.1). It is more than just a 3D model of the construction project that is used by the different designers, architects, structural engineers, and HVAC-designers. It is also used in the prefabrication process in factories, during construction works by different subcontractors, and later on in maintenance operations. The product model is a kind of virtual model of the building, and it can even be used in marketing, for example, while selling an apartment the effect of different variations can be shown to the client. In the product model, a large amount of information on the different building materials and structures are included in product libraries. Bill of quantity information is included, and when the time schedule information about the construction phases is added, it is called a 4D model. When cost estimation and cost accumulation during construction is included in the model, it is labelled a 5D-model. 130

Figure 2.1 Product model pictures of construction projects.

structures in different environments were introduced.

load bearing capacity and displacements. 2.2. Prefabricated Concrete Production During the last ten years, 500 mm (20 in.

For industry and office applications new frame systems have been developed.

3 Figure 2.1 Product model pictures of construction projects. In the Finnish national annex of Euronorm EN206 in 2004, design formulae to estimate the service life span of concrete structures in different environments were introduced. Nowadays, the design of concrete structures includes service life prediction in addition to the limit state design of load bearing capacity and displacements Prefabricated Concrete Production During the last ten years, 500 mm (20 in.) thick hollow-core slabs and wider slabs have been introduced (Figure 2.2). For industry and office applications new frame systems have been developed. They consist of over-reinforced tensioned beams that have small heights; steel-concrete composite beams have also emerged (Figure 2.3). Usually the new concrete prefabricated units are produced from high-strength concrete having a compressive strength of about 80 MPa (11.5 ksi). Figure 2.2 New prefabricated hollow-core elements. 131

(b) Steel-concrete composite delta-beam.

has been very popular, and there are factories that use SCC in nearly every

The new generation water reducing admixtures, polycarboxylates, have become

prefabricated concrete façade units (Figure 2.4).

4 (a) (b) Figure 2.3 (a) Prefabricated frame system for industrial and office buildings, and (b) Steel-concrete composite delta-beam. In prefabricated concrete unit production, self compacting concrete (SCC) has been very popular, and there are factories that use SCC in nearly every product. The new generation water reducing admixtures, polycarboxylates, have become market leaders, and use of the older superplasticizers has declined remarkably. New concrete surface treatments and graphic concrete have gained ground in prefabricated concrete façade units (Figure 2.4). The introduction of service life design has increased the use of stainless steel reinforcements in the outer surface layers of façade-prefabricated units. (a) (b) Figure 2.4 (c) New surface types in prefabricated façade elements. (a) Recycled glass, (b) blue pigment with copper, (c) graphic concrete, and (d) chemical laser painting. 132 (d)

5 During the last decade, a large number of different prefabricated concrete units for ventilation and other piping have been developed. Similarly, integration of HVAC-systems into structures has increased. For example, the cores of hollow-core slabs are used as ventilation ducts Ready-Mix Concrete Self-compacting concrete (also known as self-consolidating concrete) is used only marginally in onsite concreting in Finland. From the total volume, only a few percent are produced by SCC and then usually to obtain high quality surfaces. The other ready-mix concrete applications of SCC are concrete slabs and floors. The advantage in using SCC is the remarkable increase in concreting speed. If in the reinforcement installation a new German Bamtec-method is used, a remarkable increase in form cycle rate can be achieved, (Figure 2.5). Usually 2/3 of the slab thickness is concreted by normal concrete first; only in the surface layer of the slab is SCC used. Due to the relatively cool and moist weather in Finland, the slow drying rate of concrete structures to appropriately low moisture conditions, so that floor coverings do not suffer from the moisture in the concrete, needs to be enhanced by additional heating and drying measures. A new fast drying concrete type has been developed so that the drying time, which can exceed several months, can be shortened into a couple of weeks. In fast drying concretes the amount of cement is somewhat increased so that hydration dries part of the additional moisture. The air content of the fast drying concretes is also increased by excessive air-entrainment so that the permeability allows faster drying of the concrete structure [1]. Fast drying concretes have been proven to be quite competitive compared with traditional drying methods. Figure 2.5 Bamtec reinforcement is rolled open at the construction site. 133

6 Fiber reinforced concretes are used in Finland only in floor and slab structures to hinder shrinkage cracking and the rise of the corners of the floor due to differential shrinkage. Steel fibers are most common (40-60 kg/m 3 ) (2.5 to 3.8 lbs/ft 3 ). Computer aided mixture design of concrete structures produced by different binder types and amounts in winter or summer concreting conditions has become quite popular in Finland. With the program, the temperature distribution and strength development can be calculated, and the effects of different binders and insulation measures can be assessed. Systems for temperature measurements in hardening concrete have been improved so that they can be measured wirelessly Ecological Issues There is an ever-increasing need to create durable, environmentally friendly concrete that is also economically feasible [2, 3]. In this context, environmentally friendly concrete is defined as a concrete having a diminished environmental load during its production without losing its functional characteristics during its service-life as compared to contemporary concretes. The ecological issues affect on all aspects of concrete production from binder production, aggregate acquisition to durability and service life duration. The environmental friendliness of concrete can be achieved by partially replacing portland cement by fly ash or blast furnace slag as much as possible without compromising the durability and production technology-related properties of concrete. According to life cycle assessment and impact concrete mixes with large amounts of industrial by-products saves natural resources and the environment. By using mineral additive binders (70% blast furnace slag or 40% fly ash), the energy consumption of concrete can be lowered by 50%. Similarly, the increase of the amount of fly ash and blast furnace slag has a tendency to decrease acidification potential and SO x, and NO x emissions. In Finland, ecological aspects are considered important in the development of different structures and in the operational functions of buildings, for example, heating, cooling, and ventilation. The massiveness of concrete is a great advantage in minimizing the operational costs and environmental burden during the life span of a building. In addition, recycling of building materials has been under intensive development during recent years. The introduction of service life design has increased the use of stainless steel reinforcements in the outer surface layers of façade-prefabricated units. 134

7 3. FUTURE TRENDS It can be predicted that the ecological issues will continue to affect the building industry in increasing measures. This will include all aspects of production, the operational functions of buildings, durability properties, and recycling. However, the ecological balance sheet of concrete is relatively good. Because concrete is a cheap material, its production does not use large quantities of energy, a large portion of the CO 2 emissions liberated into the atmosphere during cement production will return back into concrete structures due to carbonation, and concrete is above all a very durable material if it is produced adequately. Therefore, the ecological impact of concrete is quite small, and the increased ecological concerns can be considered as an opportunity and not a threat because concrete s heat absorption capacity is a balancing property and a very valuable asset in diminishing heating and cooling costs and ecological burden. There are also future opportunities in using recycled materials in concrete. Increased use of blast-furnace slag and fly ash, especially in those concrete types that have very low durability demands, should be exploited more. There also exist large quantities of other recyclable materials that have been studied only sporadically such as wood ashes, organic fibers, paper, etc. The use of high-strength/high-performance concrete is slowly increasing, but there is a large unused potential in increasing these properties even more. It is relatively easy to produce self-compacting ultra-high-strength (UHSC) concrete having a compressive strength of MPa (21.7 ksi to 29 ksi) [4]. In the beginning, there will be only a few applications in the construction field, for example, in high-rise buildings and especially heavily loaded structural details. In a longer perspective, there seem to be possibilities in producing hybrid concrete structures in which only a small portion is UHSC and the major volume of the structure is cheaper normal or high-strength concrete. The extensive research going on in nanomaterials will eventually yield applications to concrete structures. Whether they will be fibers made of carbon nanotubes or self-cleaning concrete surfaces is rather difficult to predict. Concrete structures are not mounted with sensors. The situation in machines, cars, trains, and airplanes is quite different. It is obvious that in the future this will change and, for example, the lifetime management of concrete structures will be able to be monitored by sensors that send data from the structure wirelessly. Smart apartment, smart building, and smart material concepts will find applications in concrete structures and in buildings as a whole. Whether it analyses, substitution of cement in is difficult to predict. However, research on these concepts will continue in the near future. 135

8 4. SUMMARY This paper presents a concise review of the concrete advances and applications developed in Finland during the last ten years. The items discussed in the paper include product models used in design, service life prediction, new prefabricated concrete structures, new concrete surface types in prefabricated façade elements, self-compacting concrete, fast drying concretes, and ecological issues. Future trends such as recycled new materials, selfcompacting ultra-high-strength concretes, nanomaterial research, sensor technology, and smart buildings and materials are briefly discussed. ACKNOWLEDGMENTS The author expresses his gratitude to Lic. Tech. Klaus Juvas, M. Sc. Jorma Kyckling, M. Sc. Seppo Petrow, M. Sc. Arto Suikka, and Lic. Tech. Jorma Virtanen for their valuable contributions in preparing the paper. Thanks are also due for the pictures they have provided to the paper and the subsequent presentation. REFERENCES [1] Wirtanen, L., Penttala, V. Influence of temperature and relative humidity on the drying concrete. Concrete Science and Engineering, Vol. 2, No 5, p , [2] Penttala, V. Concrete and sustainable development. ACI Materials journal, Vol. 94, No. 5, p , [3] Vares, S., Penttala, V. Environmental impact of increased use of mineral additive binders in concrete. Int. Conference on Sustainability in the Cement and Concrete Industry, Lillehammer, Norway, September, 15 p., [4] Cwirzen, A., Penttala, V., Vornanen, C., Junna, K. Self-compacting ultra-high-strength concrete containing coarse aggregates. Helsinki University of Technology, Department of Civil and Environmental Engineering, Laboratory of Building Materials Technology, Report 20, 95 p. + app. 34 p.,

FAST DRYING CONCRETE

FAST DRYING CONCRETE PENTTI LUMME Abstract Several research projects have been carried out in Finland to investigate the moisture control process at the jobsite and the effect of moisture on concrete construction.