Jain College of Engineering, Engineering, Belagavi. Department of Civil Engineering.
A seminar report on,
U-BOOT U-BOOT BETON TECHNOLOG TECHNOLOG Un!er t"e G#i!an$e of,
Prof. Amey Kelkar
B%&& B%
'aveena Hiremat" (J)*+$v+ t" Bat$"&
Abstract
With depleting natural resources, deteriorating environmental conditions and tough economic times, it is important to find construction technology that is environment-friendly and cost effective. Developments in the building industry are geared toward cost effective and environmentally sustainable construction. Concrete is the most common construction material used in the world and cement is the main ingredient in concrete. However, cement manufacturing is a source of greenhouse gas emissions, accounting for approximately 7 to ! of C"# globally. $n view of these facts, it is important to reduce the environmental impacts of cement production b y reducing the %uantity of concrete that is used in construction. &his paper see's to find out whether the u-boot slab is cheaper compared to traditional solid slab used to find out the amount of concrete reduction that is achieved by use of u-boot slabs and its impact on the environment, and also compare the strength characteristics of u-boot slab and traditional solid slab. to find out the amount of concrete reduction that is achieved by use of u-boot slabs and its impact on the environment, and also compare the strength characteristics of u-boot slab and traditional solid slab. (rom the study, it was found that the use of u-boot slab resulted in a saving of concrete of about )*, and up to #+ decrease in carbon dioxide emissions when compared to a solid slab with internal beams. &he u-boot slab was also found to have bigger spans of up to )!m, while solid slabs had a maximum span of m for a given load. (or fixed spans the u-boot slab had a higher bearing capacity compared to solid slabs.
Contents 1 1
INTRODUCTION
).)ummary ).#Definition 2 U-BOOT
#.)olypropylene #.#/enefits #.01-boot technology #.2/enefits of 1-boot slabs #.+hear reinforcement of slab 3 APPLICATIONS
0.)3aft foundation 0.#$ncrease in the Head 3oom 0.0(ire resistance 0.2Concrete 4ix 4 TEST DONE ON U-BOOT SLABS
2.)3esults 2.).) ieve 5nalysis 2.).# lump &est 2.).0 Compressive strength test 5 SLAB TEST RESULTS 6 UANTITIES CO!PARISON
6.)Concrete 6.#teel 3einforcement 6.0pan Comparison 6.2conomic (easibility 5nalysis " CONCLUSION RE#ERANCES
INTRODUCTION$ 1%1 SU!!AR&
With regard to building technology, efforts are being made to reduce the concrete re%uirement in construction, increase the load bea ring capacity of structures and cut on construction costs and hence ngineers and researchers worldwide are see'ing to introduce technology that is environmentally friendly and cost efficient. $n case of hori8ontal slabs, the main obstacle with concrete constructions is the high weight, which limits the span. (or this reason, ma9or developments in reinforced concrete have focused on enhancing the span, either by reducing the weight or overcoming concrete:s natural wea'ness in tension. &o reduce the weight of the slabs, voided slabs were introduced. &he voids reduce the amount of concrete in the slab thereby reducing the weight of the slab enabling longer spans to be built. Depending on the method used to create the voids, it may also serve to reduce the cost of construction. Here 1-/oot formwor' is used as to create voids in the slabs. 1%2 DE#INATION
&he u-boot formwor' is the modular element made of recycled polypropylene for use in building lighter structures in reinforced concrete cast in the wor' site. &his new lighter structure is achieved by enclosing the u-boot within the concrete cast to create voids. labs built with u-boot can form the structural elements of v arious building systems, such as floors, rafts and so on, for both civil and industrial buildings.
Section of slabs with U-boot
Where, ) and # represent the lower and upper concrete layers respectively, while h is the height of the u boot and Ht is the total slab thic'ness.
2
U-BOOT
&he u-boot formwor' is the modular element made of recycled polypropylene for use in building lighter structures in reinforced concrete cast in the wor' site. 2%1 POL&PROP&LENE
olypropylene is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications. $t is commonly used for plastic moldings where it is in9ected into a mould while molten, forming complex shapes at relatively low cost and high volume. &his process is used to ma'e the u-boot formwor'. olypropylene is resistant to many chemical solvents, bases and acids, and does not deteriorate with time or lose its characteristics. is normally tough and flexible, especially when copolymeri8ed with ethylene. &his allows polypropylene to be used as an engineering plastic. olypropylene is economical and has good resistance to fatigue. $t has a melting point of ap proximately )6*oC.
2%2 BENE#ITS
/enefits associated with the u-boot slab are mainly environmental in nature, &he main one being the cutting down on the amount of concrete used in construction. Concrete is the most common construction material used in the world, in fact it is the second most used product on the planet, after water. Cement is the principal ingredient in concrete. Cement manufacturing is a source of greenhouse gas emissions, accounting for approximately 7 to ! of C"# globally. 1-boot slab is the reduction of plastic waste in the environment, since the u-boot units are made from recycled plastic. &hey are lighter than co mpeting materials, their transportation is easier and cheaper, they are extremely durable, and they have good resistance to chemicals, water and impact, are safe and hygienic for food pac'aging, possess excellent thermal and electrical insulation properties and are relatively cheaper to produce . $n the boo' ;Concrete slabs, 5nalysis and design< =)!2>, ?. 5 Clar' describes developments of reinforced concrete as mainly focusing on enhancing the span, either by reducing the weight or overcoming concrete:s natural wea'ness in tension. ome of the inventions include re-tressed Concrete, Hollow Core slabs, /i-axial slabs, Waffle slabs, /ubble dec' technology and 1-/oot technology.
2%3 U-BOOT TEC'NOLO(& &he u-boot formwor' is the modular element made of recycled plastic for use in building
lighter structures in reinforced concrete cast in the wor' site. $t has a truncated pyramid shape and a lower base +# x +# cm. it is composed of feet, lateral flaps and upper tips used as spacers in order to create alveolar voids in concrete massive slabs. 1nits need to be laid out on site on predisposed dec' or in a factory on a precast slab. &hey come in element height of )6, #*, #2, 0#, 06, 2*, 22, 2! cm@ feet of *, +, 7, )* cm@ flaps of )#, )2, )6, )!, #* cm.
Axonometric projection
Double u-boot
Single u-boot
Plan U-Boot )n*t
Where, / represents the width of the u-boot, h is the height and $ is the height of the u-boot feet. &he lighter structures is made up of two layers, one on top of the other, separated and connected to each other by a grid of beams at right angles which are formed when the u-boots are put in place. &he beams transfer stresses to the pillars of the structure, which allows slabs of long spans to be built. &he slabs are able to ta'e high loading and do not need internal beams, a perimeter edge beam is sufficient. 5ll that is needed is to leave a massive area around the column- called mushroom pillar- which is thic' as slab and varies on a shear stress basis. labs built with u-boot can form the structural elements of various building systems, such as double floors, floors, rafts and so on, for both civil and industrial buildings. With its high inertia levels, this building system ma'es it possible to build large scale constructions. &he biggest advantage of the u-boot is that it is stac'able. &he second innovation is the shapeA 1-boot creates a grid of orthogonal B $B beams, so the calculation of the reinforcement can be effected by any static engineer according to the uro code, /ritish standards or local norms. 2%4 BENE#ITS O# U-BOOT SLAB
&he open created by the slab give greater design freedom, and ma'es change of use easier. 3educed amount of concrete in the slab thereby reducing the environmental impacts of
cement production. 3educing the weight of the slab enabling longer spans to be built. 3eduction of plastic waste in the environment, since the u-boot units are made from recycled plastic. &he u-boot slab does not re%uire internal beams. &his results in reduced storey heights and smooth ceilings. &he u-boots are light and stac'able ma'ing them easy to transport, stoc'pile and layout. &he slab is easy to smooth once the formwor' is ta'en off and if false ceiling is re%uired the layout is faster.
2%5 S'EAR REIN#ORCE!ENT O# SLAB
&he direction of principal compressive stresses across the span of a homogeneous concrete slab ta'e the form of an arc, while the tensile stresses ta'e the form of a catenary or suspended chain. &owards the mid-span, where the shear is low an d the bending stresses are dominant, the direction of the stresses tends to be parallel to the beam axis. ear the supports, where the shearing stresses are greater, the principal stresses are inclined at a steeper angle, so that the tensile stresses are liable to cause diagonal crac'ing =4orsley, )*>. (or this reason, hollow slabs are made solid near the supports and if the slab is supported by a monolithic beam the solid section acts as the flange of a §ion. &he slabs are also made solid under partitions and concentrated loads because they cause punching shear.
labs may be divided into two ma9or categories A /eamless slabs and slabs supported on beams located on all sides of each panel. &here are many hybrid variants, and many otherwise beamless slabs have beams at the edges of the structure and around large openings, such as those made for elevators and stairways. &he u-boot slab is a form of flat, beamless slab as its weight is totally supported directly on columns. &he strength of a beamless slab is often limited by the strength in punching shear at sections around the columns. &he limited depth of the slabs ma'es the anchorage of the shear reinforcement difficult. /ecause of this problem, spearheads of structural steel have been developed for slabs at interior columns. pearheads consist of crossing steel arms welded together at a common level, to pic' up both some shear and moment load from the concrete. &hese arms which are totally within the slab thic'ness pic' up shear and moment beyond the column and bring the load to bearing on the column. &he bottom flanges of the steel shapes are extended beyond the top flanges to pic' up shear load that will exist low in the slab. &he critical section for shear on the concrete is thus moved to a larger perimeter =(erguson, )7>.
3 APPLICATIONS
3%1 RA#T #OUNDATIONS
5mongst foundations of different 'inds, raft foundations are the most common. &his is due to advantages li'e high stiffness due to static bi-directional behavior, good load distribution capacity on the ground, it absorbs stresses coming from the building with differential subsidence close to 8ero and they are easy and %uic' to layout. When stresses increase or ground be aring capacity decreases, a thic' raft foundation is needed. &his means more concrete and more pressure on the ground, and therefore building costs increases. 1-boot formwor' is designed to create a lightened (ig slab and raft foundations. "nce placed in concrete, it creates an alveolar structure, with two slabs of different thic'ness, lin'ed together by an orthogonal grid of beams of different width. $n doing so, an ideal light structure for raft foundations is carried out. tatistically it is considered as a grid of $ beams which rationally distributes masses for the purpose of inertia in order to obtain high stiffness with a minimum concrete %uantity. $n some special cases, foundation piles are not needed d ue to the combination of lightness and stiffness.
Section of raft foundation with U-boot Where, ) and # represents the lower and upper concrete layer respectively, while h is the height of the u-boot and Ht is the total height of the raft foundation. 3%2 INCREASE IN T'E 'EAD ROO!
/eams reduce headroom and impose restrictions on the use of space beneath ="ladapo, )!)>. &he absence of beams results in more spacious rooms with greater architectural freedom an easier change of use. $n addition to these advantages, beamless slabs have an economy of formwor' and once the formwor' is removed the plane surface ma'es false ceilings unnecessary. 3%3 #IRE RESISTANCE
(ire resistance as the ability of an element of construction to resist collapse,to resist penetration of flames and hot gasses while at the same time maintaining structural integrity and to 'eep the unexposed face sufficiently cool so as not to ignite materials in contact with it.&he fire resistance is a matter of the amount of concrete layer. &he fire resistance is dependent on the temperature in the rebars and hence the transport of heat. 5s the top and bottom of the u-boot slab is solid, and the rebars are placed in this solid part, the fire resistance can be designed according to demands. 5ccording to some studies carried out by the olytechnic of 4ilan, slabs lightened by means of polystyrene explode after only #* minutes when exposed to fire load. &his is due to the presence
of warm air in cavities which increases pressure and partially due to styrene sublimation. $n order to avoid slab explosions, vents are to be placed into slabs to maintain constant pressure into cavities. C$ laboratories carried out a fire test on a slab lightened by means of u-boot with a 0cm concrete cover and the structure was certified 3$ )!* minutes. 3%4 CONCRETE !I+
&he u-boot slab re%uires concrete grade 0* =)A)A#> with a slump of between )+*mm-#**mm to enable it to flow between the u-boots. &his high slump is achieved by using high-range water reducing admixtures =superplastici8ers> uperplastici8ers are used to increase the wor'ability of the con crete mix. &hese are modern types of water reducing admixtures which are very effective. 5t a given water cement ratio, this dispersing action increases the wor'ability by raising the slump from 7+mm to #**mm. the resulting concrete can be placed with little or no compaction and is not sub9ect to excessive bleeding or segregation. uperplastisi8ers produce wor'able concrete with extremely high strength due to the reduction of water-cement ratio. $t is important for the flowing concrete mix remains cohesive and suitable for pumping. "ne way of doing this is to increase the fine aggregate content by 2 to + percentage pointsA and more for very coarse sand. &his ensures cohesion and prevents segregation. 5nother approach involves the ad9ustment of fines relative to maximum aggregate si8e and cement content.
4 TESTS DONE ON U-BOOT SLABS • • •
ieves analysis lump test trength test
4%1 RESULTS
4%1%1 SIE,E ANAL&SIS
(rom the sieve analysis test, the mass of the agg regate retained in each sieve was ta'en and the data collected was tabulated as shown below. (rom the above graphs it can be seen tha t both the fine and the coarse aggregates are uniformly graded meaning that the aggregates are of approximately the same si8e
Fine aggregate grading
Graph of fine aggregate grading.
oarse aggregate grading
Graph of coarse aggregate grading
4%1%2 SLU!P TEST
We see that the concrete mix was of uniform consistency with a slump varying between )+*mm to )6*mm. this homogeneity improves the %uality and structural integrity of the cured concrete
Slump test
4%1%3 CO!PRESSI,E STREN('T TEST
&he compressive strength of the concrete varied between #.*2 mm# and 0#.06 mm# which was suitable for the specified concrete strength of 0* mm#
ompressi!e strength test
5 SLAB TEST RESULTS
&he value of deflections recorded for the two slabs was plotted against the loading app lied to the point of failure. &he solid slab failed at a loading of +6.7 E while the u-boot slab failed at a loading of 7.+E. ven though the u-boot slab was able to ta'e higher loading, its deflection was more than that of the solid slab as indicated in the graph above. &he strain curves for the two slabs show that the solid slab had higher strain values compared to the u#6 boot slab, which indicated more deformation. (rom the figures below we notice that the solid slab had more extensive crac's than the u-boot slab. (rom the test, it was concluded that the strength properties of the u-boot slab were better than those of the solid slab.
Solid slab test results
U-boot slab test results
Deflection cur!es for the solid and u-boot slabs
Strain cur!es for the solid and u-boot slabs
Failure in solid slab" crac#s
Failure in solid slab" shear
Failure in u-boot slab" crac#s
6 UANTITIES CO!PARISON
omparison of $uantities
6%1 CONCRETE
&he difference of concrete used was ).) m0 which amounts to a saving of !.76 of concrete when u-boot slab is used in place of a solid slab with internal beams. &his translates to a reduction of *.6+0 tonnes of carbon dioxide produced through the process of cement production. (or an entire structure, this reduction in carbon dioxide released to the atmosphere is significant in conserving the environment. $n cases where a solid flat slab is re%uired for the same loading and span, the saving in concrete is increased to about #+ as the thic'ness of the flat slab is more than that of a slab with internal beams.
6%2 STEEL REIN#ORCE!ENT
&he difference in the %uantity of steel used for the two slabs was not significant. &he steel reinforcement for the u-boot slab was less than that for the solid slab by ).).
6%3 SPAN CO!PARSION
&he design of the u-boot slab was possible for spans as high as )!m, with an increase of the slab thic'ness. &his is up to +* further than traditional structures. &his ma'es the u-boot slab ideal for building slabs of big spans with a high bearing capacity and is suitable for structures that re%uire significant open spaces li'e industrial or commercial buildings. Design of the solid slab failed for spans greater than !m.
6%4 ECONO!IC #EASIBILIT& ANAL&SIS
&he total cost of materials used for the u-boot slab is higher than that used for an e%uivalent solid slab by Esh )2,#6#, which is 2.# higher. &his higher cost is due to the ac%uisition of the u boot units which currently have to be imported. &he cost of the 76 u-boot units re%uired for the slab panel is Esh 02,#**, which includes the cost of importation. &his can be reduced if in future the u boots are produced locally, and since they are produced from recycled materials the cost will be reduced significantly. &he cost of labour is also slightly higher for the u -boot slab and this is attributed to the extra input in laying out the u-boots and placing of the upper reinforcement. &he cost of all other materials is lower for the u-boot slab which implies that this method of construction can be more economical in future with local production of the u-boot units.
ost comparison
ost comparison between a u-boot and a solid slab
CONCLUSION
(rom the study, it was found that the use of u-boot slab resulted in a saving of concrete of about )*, and up to #+ decrease in carbon dioxide emissions when compared to a solid slab with internal beams. &he u-boot slab was also found to have bigger spans of up to )!m, while solid slabs had a maximum span of m for a given load. (or fixed spans the u-boot slab had a higher bearing capacity compared to solid slabs. 5 comparison of the total cost for the two slabs showed that the cost of u-boot slab was higher by 2.#. 5dditional benefits of the flat u-boot slab over the beam and slab floor include the simplified formwor' and the reduced storey height. Windows can extend up to the underside of the slab and there are no beams to obstruct the light and circulation of air. &he absence of sharp corners gives greater fire resistance as there is less danger of the concrete spalling and exposing the reinforcement. &he u-boots are light and stac'able ma'ing them easy to transport, stoc'pile and la yout. &he u-boot is recommended for slabs with high loading, with live loads of +'m# and above and where large open spaces are re%uired. 1se of the u-boots is also encouraged because it is environmentally green and sustainable as it results in reduced energy F carbon emissions. &o cut down on costs of ac%uiring the u-boots, it was recommended that local production of the units
should be considered. &his will result in reduced plastic waste in our en vironment and also create employment opportunity in the production industry.
RE#ERANCES
). httpsAwn.comwhatGisGubootGtechnologyGonGcivilGengineering #. httpsAwww.youtube.comwatchvI"ey?ru(nJs. 0. httpAwww.daliform.comendisposable-formwor'-for-two-way-lightened-voidedslabsapplications-u-boot-beton. 2. K, C. 3. =)!2>. Concrete slabs analysis and design. lsevier applied science publishers. +. 'arger-Eocsis, K. =)+>. olypropylene copol ymers and blends. &echnology and engineering. 6. eville, 5. =)!>. Concrete &echnology.
