x A non-reinforced slab is two-way if it is supported in both horizontal axes. To simplify this, particles of aggregate may be considered to be suspended in the homogeneous cement. A two-way slab has moment resisting reinforcement in both directions. Solid grouting the cells of concrete blocks increases the insulating properties of a concrete block wall. is the long dimension, then moment in both directions should be considered in design. Thermal conductivity of a concrete slab indicates the rate of heat transfer through the solid mass by conduction, usually in regard to heat transfer to or from the ground. ÄWÒæh²ÜyXzòL¾Á~†ÔU) FÂR’rJÅ®ÉuÌg³ÜÔwƒÅ'ƒÁ£ƒA¢%¬££ADt4x4 êY¶•Ú@šˆ…AŒþ‚ʍ™ø4X]òáTº+£Ñ¨á䂪® In addition to filling the downhill side, this area of the slab may be supported on concrete piers which extend into the ground. For a ground-bearing slab, the formwork may consist only of side walls pushed into the ground. Energy efficiency has become a primary concern for the construction of new buildings, and the prevalence of concrete slabs calls for careful consideration of its thermal properties in order to minimise wasted energy. In many domestic and industrial buildings, a thick concrete slab supported on foundations or directly on the subsoil, is used to construct the ground floor. New York: Van Nostrand Reinhold, 1992. [8] This is a disadvantage when rooms are heated intermittently and require a quick response, as it takes longer to warm the entire building, including the slab. However, the fill material is still necessary to support the curing concrete and its reinforcement. 1983 Annual Book of ASTM Standards ( Philadelphia : American Society for Testing and Materials , 1983 ). Effective Span. C [m. 2 {\displaystyle l_{y}} Print. Campbell-Allen and Thorne (1963) derived a formula for the theoretical thermal conductivity of concrete. LOW CONDUCTIVITY AND STRUCTURAL CONCRETE Low thermally conductive concrete is proven to improve energy performance in buildings. However, the high thermal mass is an advantage in climates with large daily temperature swings, where the slab acts as a regulator, keeping the building cool by day and warm by night. This property is determined by the mass and thermal conductivity of the building material. Mud slabs typically have a moderately rough surface, finished with a float.[9]. l Concrete has low thermal diffusivity, high heat capacity, and its thermal mass is negatively affected by insulation (e.g. A slab is ground-bearing if it rests directly on the foundation, otherwise the slab is suspended. As a result, any stress induced by a load, static or dynamic, must be within the limit of the concrete's flexural strength to prevent cracking. [26] On low-budget or small-scale jobs, for instance when laying a concrete garden path, wooden planks are very common. In some cases, a naturally sloping site may be levelled simply by removing soil from the uphill site. [20] This makes them economical and easy to install for temporary or low-usage purposes such as subfloors, crawlspaces, pathways, paving, and levelling surfaces. A one-way slab has moment-resisting reinforcement only in its short axis, and is used when the moment in the long axis is negligible. %PDF-1.6 %âãÏÓ Prefabricated concrete slabs are built in a factory and transported to the site, ready to be lowered into place between steel or concrete beams. A one-way reinforced slab may be stronger than a two-way non-reinforced slab, depending on the type of load. endstream endobj startxref Mud slabs, also known as rat slabs, are thinner than the more common suspended or ground-bearing slabs (usually 50 to 150 mm), and usually contain no reinforcement. [9] In this application, a mud slab also prevents the plastic bar chairs from sinking into soft topsoil which can cause spalling due to incomplete coverage of the steel. In this case, the fill material is less important structurally as the dead weight of the slab is supported by the piers. As shown below, the thermal mass and thermal conductivity establish the thermal inertia, which causes a damping and time lag of the temperature peaks. Thermal mass is also related to thermal diffusivity, heat capacity and insulation. In modern construction, concrete slabs are usually cast above a layer of insulation such as expanded polystyrene, and the slab may contain underfloor heating pipes. hÞbbd```b``f‘@$Ó4Éþ Ì>"9CÀäJ°ø#Éö ,ëf+€II°ì°Êï@’11Äæh’ÿ}ö2012°D€ma`t䆿úÏ °5X Concrete has a relatively high thermal mass, meaning that it takes a long time to respond to changes in ambient temperature. This property is determined by the mass and thermal conductivity of the building material. where The second consideration is the high thermal mass of concrete slabs, which applies similarly to walls and floors, or wherever concrete is used within the thermal envelope. If For multi-storey buildings, there are several common slab designs (see § Design for more types): On technical drawings, reinforced concrete slabs are often abbreviated to "r.c.c. hÞÜXëoÛ6ÿWìK‹5£(¾"@M`M&kú Új"ÀÀVÚæ¿ßݑT$DZݠ]‡A I‘wäïwYäJ²Œ‰\)¦sì5˝Áa:38°Ìh‹ÇŒ¡g–htƜBn-˜È®á&‚vҒ )hUÁ(§‘fB)b…­]Ft–åÞ¯cRx…#ϤuF&cÒÓF0%rÀRÄk$SZã~F1e Êk4S>'^TÁ¯í¼~Íß/Æõ¢™]¿8׳¶iï_òõu³l÷/ÆóOõK~qw{;©§°Ì²ý}à9XŽðÅyÁ¾\_5ãö†©Lð£êö´n®oZf¼äÇu Û˅á'“êzÉdÎOæ³öðpþ­ØÓ ®±Ž’OšIZI&ù@SçÕ´æ—Í´^þ–gçõWøý0ŸV3Z¼ The actual value of k varies significantly in practice, and is usually between 0.8 and 2.0 W m−1 K−1. These slabs are generally classified as ground-bearing or suspended. Amsterdam: Butterworth-Heinemann, 2006. It is an economical and quick construction method for sites that have non-reactive soil and little slope. 1242 0 obj <>/Filter/FlateDecode/ID[<63E73177C6342E4BA0710C1B4FBDE5EB><67BE2D50D1AD7B478AF1256AB7B72198>]/Index[1225 45]/Info 1224 0 R/Length 94/Prev 690534/Root 1226 0 R/Size 1270/Type/XRef/W[1 3 1]>>stream By reducing the concrete block density by volume and producing a lower-weight block, manufacturers increase the heat-insulating properties of the blocks. [9] It is vital that the wall supporting structure is built to the correct dimensions, or the slabs may not fit. This includes use as a base or "sub-slab" for a larger structural slab. Ground-bearing slabs are usually supplemented with some form of reinforcement, often steel rebar. Garber, G. Design and Construction of Concrete Floors. [11], Levelling the site before pouring concrete is an important step, as sloping ground will cause the concrete to cure unevenly and will result in differential expansion. [9] Without reinforcement, the entire load on these slabs is supported by the strength of the concrete, which becomes a vital factor. : 47. Subsequently, Valore (1980) developed another formula in terms of overall density. The formwork is commonly built from wooden planks and boards, plastic, or steel. Print. Guide to Thermal Properties of Concrete and Masonry Systems [7] This is relatively high when compared to other materials, for example the conductivity of wood may be as low as 0.04 W m−1 K−1. [25] Plastic-tipped metal or plastic bar chairs, are used to hold the rebar away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement. 1225 0 obj <> endobj There are two common methods of filling - controlled fill and rolled fill. x On-site concrete slabs are built on the building site using formwork - a type of boxing into which the wet concrete is poured. As shown below, the thermal mass and thermal conductivity establish the thermal inertia, which causes a damping and time lag of the temperature peaks. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving (see below).[1][2]. This is usually aided by a membrane, either plastic (temporary) or a liquid compound (permanent).[13]. R. C [K/W] is the thermal resistance of the concrete section, L [m] is the thickness of the section, in the direction of the heat flux, k. C [W/(m.K)] is the concrete thermal conductivity and .

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