AN ECONOMIC PERSPECTIVE OF ADVANTAGES OF USING LIGHTWEIGHT CONCRETE IN CONSTRUCTION

S. Kivrak, Anadolu University, Turkey

M. Tuncan, Anadolu University, Turkey M. I. Onur, Anadolu University, Turkey G. Arslan, Anadolu University, Turkey O. Arioz*, Anadolu University, Turkey

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31st Conference on OUR WORLD IN CONCRETE & STRUCTURES: 16 – 17 August 2006, Singapore

AN ECONOMIC PERSPECTIVE OF ADVANTAGES OF USING LIGHTWEIGHT CONCRETE IN CONSTRUCTION

S. Kivrak, Anadolu University, Turkey M. Tuncan, Anadolu University, Turkey M. I. Onur, Anadolu University, Turkey G. Arslan, Anadolu University, Turkey O. Arioz*, Anadolu University, Turkey

Abstract

The developments of complex structures, high-tower buildings, large-sized concrete structures, etc. in recent years result in a need for better concrete performance. Reducing the self-weight of the structures is vital for the structural safety. For this purpose, lightweight concrete (LWC) has been used successfully for both structural and non-structural applications for many years. The use of LWC is continuously increasing for many structural purposes all around the world. Good thermal insulation, better durability and reduction in self-weight of the structures are well recognised benefits of this material. Furthermore, the utilisation of LWC is highly essential in terms construction costs. In this study, the possible advantages of using LWC in construction have been scrutinised, and the benefits of using this material, especially in earthquake regions such as Turkey, have been examined.

Keywords: Lightweight concrete, economic benefits, lightweight aggregate

1. Introduction Concrete is one of the most commonly used construction materials. Both technical properties and economic advantages of this material make it to be a widely used material for structural purposes in construction technology. Concrete is generally manufactured at site by mixing together cement, water, aggregates and if required admixtures. Concrete should satisfy performance requirements in both fresh and hardened state. Concrete should be workable without segregation and bleeding in its fresh state and it should be strong, durable and impermeable in its hardened state. The compressive strength of concrete is generally considered to be the most important property which is taken as an index of the quality of concrete [1]. Lightweight concrete (LWC) has been used successfully in various constructions for many years [2-7]. The main reason of using LWC for structural purposes is to reduce the self-weight of concrete structures. Reducing the dead load of the structure is very important in earthquake regions, for tall buildings, and special concrete structures. The density of LWC is approximately 80 percent that of normal weight concrete. The density of structural LWC typically ranges between 1440 and 1840 kg/m3, whereas these values vary between 2240 and 2400 kg/m3 for normal weight concrete. Therefore, the most important advantage of using LWC is the possible decrease in the construction costs due to the reduction in weight of the structure. The use of LWC in the field of precast concrete structures also facilitates the transport of concrete elements [8]. The other main purpose of LWC production is its good thermal insulation when compared to ordinary concrete.

In the following sections of this study, the economic advantages of using LWC in construction have been scrutinized. Case studies were also performed in order to examine the cost advantages of this material.

2. Lightweight aggregate Lightweight aggregate (LWA) is the aggregate of low bulk specific gravity [10]. Some LWAs occur naturally while the remaining can be manufactured. Examples for natural aggregates are diatomite, pumice, scoria and volcanic tuff. The use of natural aggregates is limited because of the absence of this material in most areas. In Turkey, pumice concrete is used for some residential construction and there are many deposits of diatomite in some of the regions in Turkey. Expanded clay aggregate, which is produced from clay by heat treatment, is an example for artificial LWA. One of the most important characteristics of lightweight aggregate is its high internal porosity which leads to maintain a low apparent specific gravity [11]. Generally, smaller particles have higher specific gravities than coarse ones. It should also be noted that high porosity may result in lower strength, and as a rule, low heat conductivity. Thus, lightweight concretes used in insulation have lower strengths [12].

3. Lightweight concrete (LWC) LWC is produced mainly by three methods [9]:

Using lightweight aggregate of low specific gravity instead of normal weight aggregate such as gravel or crushed aggregate.

By introducing large voids within the concrete or mortar mass. This type of concrete is named as aerated, cellular, foamed, or gas concrete.

By omitting the fine aggregate from the mix to produce no-fines concrete. Typical ranges of densities of concretes made with various lightweight aggregates are illustrated in Fig. 1 [9]. Insulating Concrete Moderate Strength Structural Concrete Concrete Sinter-Strand Expanded Clay or Shale, Pulverized-Fuel Ash, and Expanded Slag Rotary-Kiln Expanded Clay, Shale and Slate Scoria Pumice Perlite Vermiculite 400 600 800 1000 1200 1400 1600 1800 kg/m3

28-day-Air-Dry-Density Figure 1. Typical ranges of densities of concretes made with various lightweight aggregates Gambhir [1] explained some characteristics of LWC as follows:

Low density: The density of LWC is much lower than that of ordinary concrete. High strength: The compressive strength of cellular concrete is high enough in relation to its

density.

Thermal insulation: LWC has a lower thermal conductivity when compared to ordinary concrete.

Fire resistance: LWC may protect other structures from the effects of fire due to its low thermal conductivity.

Sound insulation: Sound insulation is better in LWC. Speed of construction: The construction speed could be faster by using LWC in precast

construction. Economy: Saving in reinforcement steel and cement could be obtained that result in a

reduction in construction costs. Quality control: Prefabrication of LWC units can lead to better quality control in construction.

The use of LWC is increasing rapidly in many structural and non-structural applications owing to its various advantages explained above [13]. There are several applications of LWCs in construction fields. It can be used as load bearing walls, precast floor and roof panels, partition walls, bridge decks, piers and beams, slabs in concrete buildings, long span viaducts, etc. The use of LWC is not wide in Turkey. Obviously, the mix design of LWC is different from that of ordinary concrete since the aggregates of LWC and ordinary concrete are quite different from each other. For instance, the water absorption values of LWC aggregates are much higher than those of ordinary ones. This can affect the performance of concrete due to the fact that it is difficult to maintain specific water content during the casting [14]. Therefore, it is recommended that first to mix the aggregate with at least one-half of the mixing water and only then add the cement into the mixer [9]. Structural LWC which should have strength greater than 17.0 MPa has been a niche product for many years [15]. With the use of structural LWC, the size of columns, footings and other load bearing elements can be reduced in concrete structures. Reductions in size of structural elements, reinforcement steel and volume of concrete bring about lower construction cost.

4. Economic advantages of lightweight concrete The cost of LWC by volume is usually higher when compared to conventional concrete. However, total construction costs can be reduced by the reductions in the size and weights of the structural elements and reinforcement steel. Cost savings could be obtained both in the design and construction stages. In the design phase, cost savings could be achieved by lower steel requirements and reduction in concrete volume. In construction phase, the lower density of LWC can lead to cost savings by reduction in transportation costs and easier handling [16]. In building construction, longer spans could be designed and additional floors could be added to existing structures when LWC is used. Smaller footings, fewer piles, smaller pile caps and less reinforcing are required by decrease in foundation loads. In bridge construction, a wider bridge deck could be placed on existing structural supports. LWC can be used to create longer bridge spans. When compared to ordinary concrete used in these structures, economic advantages could be achieved by the use of LWC [17]. In precast construction, cost savings could be obtained in transportation costs owing to light weights of the products since these costs are directly related to the weight of concrete product. The first LWC building in history was the gymnasium addition to the Westport High School in Kansas City (1922). In San Francisco – Oakland Bay Bridge, a cost saving of $3 million was estimated by the use of LWC in the construction of upper deck of the bridge [18].

5. Case studies In this part, simple case studies regarding the use of LWC and normal weight concrete on three special structures have been briefly performed. Selected structures which were chosen from the examples in Sta4CAD (Structural Analysis for Computer-Aided Design) program were analyzed in order to investigate some economic advantages of using LWC in these structures. It should be noted that some dimensions of these structures were re-designed. Educational examples taken from this program consisted of an 8-storey car park, 18-storey shopping centre building, and 22-storey residential building. Formwork plans and three-dimensional views of these structures are illustrated in Figures 2, 3 and 4. Structural analyses were performed according to the Turkish earthquake code and TS 500 (Turkish Standards – Building Code Requirements for Reinforced Concrete). Structures were assumed to be constructed in the first seismic zone in Turkey. In the analysis, the dimensions of the structural elements were not changed and only the amounts of reinforcement steel by using normal

weight concrete (having 2.4 t/m3 density) and LWC (having 1.8 t/m3 density) were calculated. Concrete class was selected as C25.

Figure 2. Three-dimensional view and formwork plan of the multi-storey car park

Figure 3. Three-dimensional view and formwork plan of the shopping centre

Figure 4. Three-dimensional view and formwork plan of the residential building

According to the analysis, it was found that if the centre of gravity does not coincide with the centre of rigidity of the buildings, higher amount of reinforcement steel was required by using normal weight concrete when compared to LWC. It should be noted that changes in the amount of slab reinforcement steel were found negligible. In each analysis minimum reinforcement steel according to the codes was used in slabs therefore no changes in the amounts of reinforcement steel in slab elements were observed. Reductions in the amount of reinforcement steel were generally observed in columns and beams, especially in longitudinal steels of columns (Table 1). It is clearly seen from Table 1 that amounts of total reinforcement steel are lowered by using LWC in these structures. LWC reduced the dead load of the structures resulting a decrease in reinforcement steel. Savings in reinforcement steel also bring about savings in total construction costs. According to the results of the analyses of this study, total reductions in reinforcement steel were found to be 5.4, 2, and 1% for residential building, shopping centre, and car park, respectively. It is obvious that using LWC will also reduce the dimensions of the structural elements of these structures and therefore reduce the volume of concrete if further analysis would be performed. It should also be marked that the cost of soil improvement for the buildings when using LWC will be significantly reduced. Table 1. Reduction in amount of reinforcement steel Reduction (%) Building Columns Beams Slabs Total Car park 0.6 2.5 Negligible 1 Shopping centre 2.3 1 Negligible 2 Residence 6.0 2 Negligible 5.4

6. Conclusions

In this study, the use of LWC in construction technology is scrutinized. It can be concluded that the possible advantages in cost savings could be obtained both in design and construction stages. LWC lowers the dead load of the structures thus, lower amount of reinforcement steel is required. As a result, savings in total construction cost could be obtained. Simple case studies are illustrated in order to show the benefits of using LWC in various constructions. The analyses in this study are focused on the reductions in the amount of reinforcement steel. If normal weight concrete is used in these structures, the cost of soil improvement will obviously have an important share in the total construction cost. LWC allows smaller loads being transmitted to the substructures and the foundations of the buildings by reducing the dead load of the structures. Therefore, the cost of soil improvement for the buildings when using LWC will be significantly reduced. Additionally, the amount of reinforcement steel in foundations will also be considerably reduced by the use of LWC. The foundations were not taken into account in scope of this investigation. Further researches on the cost advantages of using LWC with a more detailed study are also required. REFERENCES [1] Gambhir M.L., Concrete Technology, Tata McGraw-Hill Publishing Company Limited, Fourth

Reprint 1993. [2] Chen B., Liu J., Contribution of hybrid fibers on the properties of the high-strength lightweight

concrete having good workability, Cement and Concrete Research, 35 (2005) 913-917. [3] Gao J., Sun W., Morino K., Mechanical properties of steel fiber-reinforced, high-strength,

lightweight concrete, Cement and Concrete Research, 19 (4) (1997) 307-313. [4] Wasseman R., Bentur A., Effect of lightweight fly ash aggregate microstructure on the strength of

concrete, Cement and Concrete Research, 27 (4) (1997) 525-537. [5] Balendran R.V., Zhou F.P., Nadeem A., Leung A.Y.T., Influence of steel fibres on strength and

ductility of normal and lightweight high strength concrete, Building and Environment, 37 (2002) 1361-1367.

[6] Merikallio T., Mannonen R., Penttala V., Drying of lightweight concrete produced from crushed expanded clay aggregate, Cement and Concrete Research, 26 (9) (1996) 1423-1433.

[7] Mays G.C., Barnes R.A., The performance of lightweight aggregate concrete structures in service, the Structural Engineer, 69 (20) (1991) 351-361.

[8] Campione G., Mendola L.L., Behavior in compression of lightweight fiber reinforced concrete confined with transverse steel reinforcement, Cement and Concrete Composites, 26 (2004) 645-656.

[9] Neville A.M., Properties of Concrete, The English Language Book Society and Pitman Publishing, 3rd Edition, 1981.

[10] ACI, Cement and Concrete Terminology, Publication SP-19, American Concrete Institute (1985d). [11] Chi J.M., Huang R., Yang C.C., Chang J.J., Effect of aggregate properties on the strength and

stiffness of lightweight concrete, Cement and Concrete Composites, 25 (2003) 197-205. [12] Popovics S., Concrete Materials: Properties, Specifications and Testing, Noyes Publications,

Second Edition, 1992. [13] Balaguru P., Foden A., Properties of fiber reinforced structural lightweight concrete, ACI Structural

Journal, 93 (1) (1996) 62-78. [14] Babu K.G., Babu D.S., Performance of fly ash concretes containing lightweight EPS aggregates,

Cement and Concrete Composites, 26 (2004) 605-611. [15] Special Concretes: Creating new markets, New Zealand Concrete, March 2002. [16] Sylva G.S., Breen J.E., Burns N.H., Feasibility of utilizing high-performance lightweight concrete

in pretensioned bridge girders and panels, Research Report 1852-2, Texas Department of Transportation, January 2002.

[17] Ries J.P., Holm T.A., A holistic approach to sustainability for the concrete community, Lightweight concrete – two millennia of proven performance, Expanded shale, clay & slate institute (ESCSI).

[18] Expanded shale, clay & slate institute (ESCSI), Lightweight concrete- history, applications, economics.