الرئيسية
أحدث الصور
من طرف بحث تخرج مقدم من قبل الطالب احمد جلال خليل جدوع بعنوان
الخرسانة الخلوية عالية المقاومة
There are three broad methods of producing lightweight concrete, in the first porous lightweight aggregate of law apparent specific gravity is used instead of ordinary aggregate whose specific gravity is approximately 2.6, the resultant concrete is generally known by the name of the lightweight aggregate used.
The second method of producing lightweight concrete relies on introducing large voids within the concrete or mortar mass, these voids should be clearly distinguished from the extremely fine voids produced by air entraining, this type of concrete is variously known as aerated, cellular, foamed or gas concrete[ 3 J .
The third means of obtaining lightweight concrete is by simply omitting the fine aggregate from the mix so that a large number of interstitial voids is present. Coarse aggregate of ordinary weight is generally used[ 3 J .
Cellular Concrete
Cellular concrete is a cementations paste of neat cement or cement and fine sand with a multitude of micro / microscopic discrete air cells uniformly distributed throughout the mixture to create a lightweight concrete .It is commonly manufactured by two different methods :-
METHOD A: consists of mixing a pre-formed foam [ surfactant J or mix-foaming agents mixture into the cement and water slurry. As the concrete hardens, the bubbles disintegrate leaving air voids of a similar size [ 4 J .
l.Jntroduction
In concrete construction, self-weight represents a very large proportion of the total load on the structure, and there are clearly considerable advantages in reducing the density of concrete. The chief of these are the use of smaller sections and the corresponding reduction in the size of foundations. Furthermore, with lighter cC!ncrete the form work need withstand a lower pressure than would be the case with ordinary concrete , and also the total weight of materials to be handled is reduced with a consequent increase in productivity, light weight concrete also
~IJ I
gives better thermal insulation than ordinary concrete, the practical range of
densities of lightweight concrete is between 300 and 1850 kg/m3[ 1 J ,[ 2 J .
METHOD B :known as Autoclaved Aerated Concrete [ AAC} consist of mix alime , sand, cement, water and an expansion agent. The bubble is made by adding expansion agents [ aluminum powder or hydrogen peroxide] to the mix during the mixing process, this create a chemical reaction that qenerate gas, either as hydrogen or as oxygen to from a gas bubble structure within the concrete, the material is then formed into molds. Each mold fell into one-half of its depth with the slurry. The gasification process begin and the mixture expands to fell the mold above the top, similar to baking a cake . After the initial setting it is then cured under high-pressure-steam [180 to 210 Co /356 to 410 F] " autoclaved "for a specific amount of time to produce thefinal micro/ macro-structure [ 1 ] , [ 4 ] .
Recently I a direction to concrete composition prepared by using aqueous gels [ aquagels ] is being considered as all or part of the aggregate in a concrete mix. Aquagel spheres, particles or pieces are formed from gelatinized starch and adding into a matrix. Starch modified or unmodified such as wheat corn, rise, potato or a combination of a modified or unmodified starches are examples of aqueous gels. A modified starch is a starch that has been modified by hydrolysis' or dextrinization . A gas is another material that can create a pore or cell in concrete. During the curing process as an aquagelloses moisture, it shrink and eventually dries up to form a dried bead or particle that is a fraction of the size of the original aquagel in the cell or pore in the concrete. This results a cellular, lightweight concrete. These cells may account for up to 80% of the total volume. Weight of the concrete mixtures range from 220 kilograms per cubic meter [ 14/bs. Cubic foot] to 1922 kilograms per cubic meter [ 120 /bs. Cubic foot] and compressive strengths vary from 0.34 megapascals [ 50 pounds per square inch] to 20: 7 mega pascals [ 3000 pounds per square inch] [1].
High Performance cellular concrete
High- performance cellular concrete [ HPCC] has all the properties of cellular concrete and can achieve 20 - 40 Mpa [ 8000 psi] . Higher strengths can be produced with the addition of supplementary cementations materials. Density and strengths can be controlled to meet specific structural and nonstructural design
requirements. Where as in conventional cellular concrete these cannot be achieved.
High-performance concrete is defined as " concrete which meets special performance and uniformity requirements that cannot always be achieved routinely by using only conventional materials and normal mixing, placing and curing practices. II The requirements may involve enhancements of characteristics such as ease of placement and compaction without segregation, long term mechanical properties. density, volume, endurance, stability, or severe or hostile
environments [ 5 J .
Density is the best characteristic feature of cellular concrete. The lowest densities being used for fills and insulation; and the higher densities being used for structural application, leading to a substantial reduction in the dead weight of a structure. 0.028 cubic meter [ one cubic foot J of foam in a matrix replaces 28.30 kilograms [ 62.4 Ibs. J of water, or O. 028 cubic meter [ one solid cubic foot J of aggregate weighting 74.84 kilograms [ 165 Ibs. per cubic foot J . HPCC has excellent insulation properties that significantly reduces the transfer of heat through the concrete member. This bubble is accountable for a superior freezing and thawing resistance and thermal reduce conductivity, low water absorption, high tensile strength, high fire resistance and sound retention, and corrects deficiencies in the sand that causes bleeding . Forming, conveyance, placing and finishing systems for cellular concrete are no different than current methods in the construction industry [ 6 J .
HPCC also has the advantage of being conducive to mobile and remote projects where building materials are difficult to obtain or reach [ 1]. The advantages derived by the use of superelasticizers include production of concrete having high workability for easy placement and production of high strength concrete with normal workability but with a lower water content. To enhance cellular concrete mineral admixtures were added, many properties of concrete can be favorably influenced I some by physical effects associated with small particles which have generally a fine particle size distribution than Portland cement and others by pozzolanic cementations reaction [ 7 J .
Aim of project
This project aimed to product cellular concrete by using local materials and simple technology . Industrial sand used (they are a small beads J when soaked in water became larger and absorb water I when dried they loss the water J and leave bubbles inside concrete) . Silica fume and superplasticizer used to enhance compressive strength of concrete.
CHAPTEOTWo
Literature Review
2. Literature Review
The literature review will describe the previous investigations concerning the aim of this project:
The research [1} classify the density of light weight concrete and show that density is the best characteristic feature of cellular concrete. The lowest densities being used for fills and insulation; and the higher densities being used for structural applications, leading to a substantial reduction in the dead weight of a structure. 0.028 cubic meter of foam in a matrix replaces 28.3 kilograms of water.
In research[ 4 }, lime, cement .silica and sulfonated hydrocarbons were used to produce foamed concrete masonry blocks for insulation with a dry density between 670 - 850 kg 1m3 and having a compressive strength between
( 2.5 - 3.0 )Mpa .
[ 5 ) show a series of concrete mixes was made using various combinations of lightweight and normal weight aggregates. Properties measured include expansion, indirect tensile strength and compressive strength. Test results indicate no significant difference in performance between concrete mixes with lightweight coarse aggregate combined with either reactive, non reactive, or light weight fine aggregate.
The research [ 6} use a new method of curing was proposed in the early nintis . The main idea consists in the substitution of part of the aggregates by prewetted light weight aggregates ( LWA). The water stored in the light weight aggregates' is on the disposition of the cement paste. During drying and hardening water from the light weight aggregate is absorbed by the cement paste by capillary suction and condensation .As the hydration proceeds newly built hydration products fill micro cracks, improving the density of the cement paste. In order to show the improved properties of the concrete including partially light weight aggregates macroscopical and microscopical investigations were performed. The I most important results is presented.
The research! 8 J described the use of near-saturated light weight aggregatas a replacement for a portion of the normal weight aggregate in high performance concrete in order to eliminate the autogenous shrinkage can occur. The work show that the addition of saturated light weight aggregate to the concrete does not appear to have any advense effects on the mechanical properties of the concrete andin most instances J small improvement have been
noted.
The focus! 9 J paper is to show that good quality structural light weight concrete with sound engineering properties and high durability characteristics can be produced for a wide range of infrastructure and global applications utilizing structural light weight aggregates and a total binder content of no more than 350 kq/m", the Portland cement contents of this concretes was limited to no less than 250 kg/m3J but the concrete matrix was supplemented by a small amount of a highly reactive pozzolan such as silica fume, and the balance was made up with fly ash and/or slag.
10 J indicate that wing expanded polystyrene beads will produce air - voids in concrete J and the result indicate that this cellular concrete have a fair compressive strength with a very good thermal insulation and low thermal expansion in addition to high moisture protection.
CHA.PTER THREE
Experimental work
3 . Experimental work
3.1 Material
3.1.1 Cement
Ordinary Portland cement, Turkish cement (Adana) was used in this work
. Tables (3 -1) and ( 3 - 2) show the chemical and physical properties of cement used. tests result indicated that the adopted cement conformed to the Iraqi specification No. 5/1984.
Ta~/e ( 3 -1) : Chemical composition and main compounds of cement
3.1.2 Fine Aggregat
River natural sand with grading limits Bs.882/1992 was used throughout this work.
Table ( 3 - 3 ) showed the sieve analysis of fine aggregate grading was within the requirements of es. 882/1992.
Table ( 3 -3) grading of fine Aggregate
3.1.3 superplasticlzer - high range water reducing admixture (HRWRA) :
A superplasticizer type sulphonated melamine formaldehyde condensate ,which is known commercially as Melment UO, was used throughout this study as a high range water reducing admixture. The material was prepared as a solution .the technical description shown in table (3 - 4 ) .
Table ( 3 -4) Technical description of superplasticizer
3.1.4 Silica fume
Silica fume is an extremely fine, spherical powder that is used as an additive for improving concrete performance .per ASTM 1240 definition, it is "a very fine pozzolanic material, composed mostly of amorphous silica prodused by electric arc furnaces as by _ product of the production of elemental silicon or ferro _ silicon alloys". The normal addition rates of silica fume range between (6 0 10) % by weight of the cementation content of the mix. In certain shotcrete and gunite application, this percentage has been increased to between 12 0 15 % to make the mix even more cohesive and further reduce the rebound [ 11 J .Due to its pozzolanic nature, silica fume can be used to enhance the qualities of both fresh and hardened concrete. This improvement is due to the formation of additional calcium silicate hydrate ( CSH ) binder, through the reaction of the silica fume ( Si02) with the free lime ( CaOH ) present in the cement . Silica fume is very rich in silicon dioxide ( > 85% ) .
3.1.5 Industrial sand
They are a very small beads of gelatin material when soaked in water, they became larger their diameter between ( , r -18) mm . After the specimen is dried they return to their ordinary volume, very small .
3.2 Mixing I Casting and Curing procedure
Hand mixing used in this project. First the cement mixed with the industrial sand, to coat it with cement, other materials ( dry sand I silica fume) mixed then in a large pan. The required quantity of water was mixed with the superplasticizer and then added to the mix. Mixing continue to get a uniform mix. Casting was carried out without vibrating and the surface of concrete was then struck with trowel. After that the specimens demoulded after one day I half of the specimens were stored in water as a curing condition to the time of testing, and the others were covered with nylon sheet and retained to time of testing.
3.3 Experimental program testing:
The compressive strength test was determined according to ASTM C 39 [13} r 100 mm cubes were tested using testing machine with capacity of ( 2000 KN) . The specimen used in oven 60• C between ( 2 - 4) hours before testing. The average of three cube adopted at each test.
Absorption test according to ASTM C 642 [14} was determined at age of 28 days, three cubes ( 100 mm ) were taken from tap water tank and put in the oven ( 105 i: 5 C ) for 24 hrs'. Then they were weighed. The following calculation were
made:
Absorption % = [( wet sample - dry sample) / dry sample }*100
28 days air dry density for ( 100 mm ) cubes were used to determine density according to ASTM C 567.
12
I
CHAPTER FOUR
Results and Discussion
4 . Results and Discussion
Tables { 4.1 to 4.8}show mix properties and the result of the testing specimens. Figures { 4.1 to 4.4 } indicate the relationship between the parameters measured in this project.
Discussion :-
4.1 Compressive strength
In general Light Weight Concrete {LWC} are not as strong as normal weight concrete, and thus the concrete strength will depend on a number of consideration. strength will depend on the type and quality of aggregate used, the size of fraction used, the amount of aggregate used, the type and quality of the binder used, and type of admixture.
Compressive strength were measured up to 56 days as shown in table 4.3 , 4.4 and in figs {4.1 and 4.2} the result indicate that there are a difference in the compressive strength, were the percentage of the industrial sand is changed from 0.5 to 2 .
The results show also increasing of compressive strength with age. for mix 1, the percentage of compressive strength from 7 days to 56 days is about 24% and about 21.5 % for mix 2 and so on . this increasing not much big, because the absence of silica fume help the concrete to get strength at early ages.
From the results also .thot the compressive strength affected by the type of the curing. Soaking in 23°C water gave higher results. But still the compressive strength for self using good when compare the specification.
The compressive strength between { 20.87 -15.22 }Mpa will be considered as structural concrete, and compressive strength between { 11 - 18} Mpa as moderate and below that will be insulation.
From table { 4 - 8 }, when compared with concrete block { density 2400 kg/m3} cellular concrete mixes {densities 1200 -1600 kq/m" } give higher compressive strength.
4.2 Absorption
Results for the different concrete mixes are shown in table ( 4.5 ) and Fig ( 4.3) .
The absorption of the mixes are between 11.9% to 14% . Comparing with concrete block. It is clear that the absorption are in agreement with the specification, although the mixes have densities more less than concrete block.
Table ( 4.
show the specification of concrete block and thermo stone according to Iraqi specification ( No. 1077/1987 ) ( 1441/2000) respeetively. From the table .and , when compared with thermo stone the mixes result are very good.4.3- 28 days - air dry density :-
The 28 - Air dry density of all mixes are percentage in table ( 4 - 6) . Results of the different concrete mixes show that using of the industrial sand and getting the air bubbles inside the concrete reduce the density. Mix 1 gave 1600 kg/m3 when the proportion of the industrial sand to ordinary sand 1:0,5, but when this proportion increased the density was reduced to 1200 kg/ m3 .
Act manual, indicate the relation between compressive strength and densities. concrete with less than 350 kg/m3 will have a strength between 1-3 Mpa. Densities between (900-1850) will give strength more than 20 Mpa. The result in this project are with accommodation of the Act manual.
4.4 Thermal Conductivity
The importance reason for production of cellular concrete is thermal insulation. Table ( 4. 7 ) show the results.
According to Act [ 15 J , thermal conductivity factor ( k) calculated from the equation :-
K :- thermal conductivity factor w/m.kcal
:- dry density kg/m3
Comparing with ordinary concrete ( k = 1.45 w/m.k cal) I the results show good properties of thermal insulation.
4.5 Self Curing
The essential way to achieve the designed properties of concrete is proper curing. This mean avoiding water evaporation at the surface of the concrete member and supplying water from the exterior. If enough water was available to cement paste for hydration to proceed I the concrete will achieve excellent properties. The concrete with w/c lower than 0.40 in combination with the high cement content and to addition of silica fume I the concrete will show a high rate of hydration and the well known relatively high compressive strength of early age. So creating a water supply in the concrete which is independent of the of the environment is a good idea. The water bubbles used in this research contain amount of water I in which will supply the concrete the desired amount of water for hvdration . The compressive strenqth not much affected.
Results: -
Table 4.1 : Mix proportion for natural sand to industrial sand by volume
,
CHAPTER FIJIE
Conclusions
5. Conclusions
Baste on the results of this project the following conclusions are drawn:
1- Cellular concrete be product using cement .sand .industrial sand, silica fume and superplistaziar .
2- At 28 days the compressive strength for mixes when cured in (23°c) water are
between (8.8 -19. 7)Mpa and ( 8.28 -15.67 ) Mpa for self curing according to
mix proportion. When the cells increased compressive strength decreased.
3- At 56 - days the compressive strength for ( 23 ° C) water curing are
( 10.87 -20.87 ) Mpa .
4- Absorption for the mixes are between ( 11.9 % -14 % l . comparing with thermiston ( 45 % ) , these results are very good.
5- 28-days dry density are from ( 1200 -1600 ) kq/m? .
6- All the mixes can be considered as structural concrete.
7- Adding silica fume and superplasticizer increase the compressive strength of concrete.
8- Cost of this type of concrete same as concrete but cheaper the therrniston .
References
References
3. AM Neville. II Properties of concrete II 2003 .
5. S. R. Boyd I T. A. Holm I and T. W. Bremner II performance of structural light weight concrete made with a potentially reactive natural sand "I sixth CANMET lAC! International con terence on durability of concrete. June 2003
6. S. Weber and H. W. Reinhardt II Modeling the internal curing of high - strength concrete using light weight aggregates ".
7. Concrete admixtures hand book properties I science and technology V. S . RAMACHANDRAN -1984.
8. G. C. Hoff II Internal curing of concrete using light weight aggregate "I sixth CANMET lAC! International conference on durability of concrete. June 2005
9. R. N. Swamy II lightweight aggregate concrete" : The Flagship of sustainable construction ""I sixth CANMET lAC! International conference on durability of concrete. June 2003
10. Nadia S. I Daad M. II using polystyrene in production of cellular lightweight masonry concrete having high moisture protection [ZJ vol. 14 I NO.4 I 2003
مجلة علوم الرافدين
11. II Typical characteristics of silica fume" From Internet I 2007
.المواصفة القياسية العراقية رقم ( 5 ) لسنة 1984 السمنت البورتلاندي 12-
13. ASTM C39 II Standard test method for compressive strength of lightweight concrete cube. Annual book of ASTM I standards I vol. 04. 02 I 1989.
14. ASTM 642 "Standard method for specific gravity I Absorption and voids in hardend concrete" Annual book of ASTM I standards I vol. 04 . 02 I 1989.
15. AC! Manual of concrete practice 1985 part 1 . Materials and general properties of concrete ( P.213 R.79 ) .
1. II High - strength structural lightweight concrete [ZJ From Internet I 2003 .
2. ACI Manual of concrete practice. Part 1 . Guide for use of admixtures in
i ~ concrete. American institute. U.S.A. 1985 .
4. Nadia S. I Daad M. II Foamed concrete masonry blocks using local raw materials II Raffider Jurnal I Mosul University vol. 10 I No.2 .2002.
