Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : compressive strength


Enhancing of Crushed Brick Aggregate Concrete by Adding Alkalis

S.A. Hameed

Engineering and Technology Journal, 2017, Volume 35, Issue 6, Pages 554-559

The process of recycling the waste of construction materials increased in most countries in the world, because of the huge quantities of waste materials result from demolition that will effect of the environment and increase landfills. This research aims to examine the recycle clay bricks aggregate in concrete mix instead of coarse aggregate and to study the effect of alkalis on this kind of concrete by partial replacement of recycle clay bricks aggregate (RCBA) instead of natural coarse aggregate. A cubic, cylinder and prisms specimens were casted to estimate the mechanical properties like dry and wet density, compressive strength, splitting tensile strength and modulus of rupture for this concrete. The results shows the increasing of RCBA will decrease the compressive strength, splitting tensile strength and modulus of rupture but the addition of alkalis with 20% of mix water will increase the workability and reduce the mix water and increase the wet and dry densities, and reduce the compressive strength and splitting tensile strength and the modulus of rupture.

Mechanical Properties of Fiberous High Performance Lightweight Aggregate Concrete

H.K. Ahmed; W.I. Khalil; M.D. Subhi

Engineering and Technology Journal, 2017, Volume 35, Issue 3, Pages 229-238

Structural lightweight aggregate concrete solves weight and durability problems in buildings and structures. Recent advanced in material technology have accelerated the development of high performance concrete using lightweight aggregate. The main objective of this research is to produce high performance lightweight aggregate concrete reinforced with polypropylene and to study the mechanical properties of this type. The effect of various factors such as type of fiber and volume fraction of fibers also has been investigated. The experimental work included the use of pumice as coarse and fine lightweight aggregate, superplasticizer and silica fume to produce high performance lightweight concrete. Several trial mixes were examined to determine the proper proportion of the concrete constituent. Three types of polypropylene with different volume fraction were used. The procedure also includes studying the compressive strength, splitting tensile strength, flexural strength and static modulus of elasticity. The test results shows that the addition of all types of polypropylene fiber results in significant improvement in most mechanical properties compared with reference concrete specimens at different ages except compressive strength it was improved at Vf =0.25% and decrease at Vf =0.75%.

Effect of Using Plastic and Rubber Wastes as Fine Aggregate on Some Properties of Cement Mortar

Basil S. Al-Shathr; Iqbal N. Gorgis; Rafid F. Motlog

Engineering and Technology Journal, 2016, Volume 34, Issue 8, Pages 1688-1699

This research describes the production of lightweight cement mortar using four types of fine aggregates including chopped rubber tires, chopped plastic wastes, a mixture from the previous types by 1:1, and a mixture composed from substitution of 10% from the previous type by natural sand. Theuseofthese wastes has rolein getting rid oftheir hugequantitieswhich constitute a fundamentalenvironmental problembecause of the difficulty of itsdegradation.
Four, cement to aggregate ratios have been used. They are1:0.5, 1:0.7, 1:1, and 1:1.2 for each aggregate type mentioned above, with changing w/c ratio and superplasticizer content to have a constant flow of about 23%. Also, the effect of curing samples by different methods, including continuous submerge in water, autoclave curing for 3 hours, and carbonation curing by 50% and 100% CO2 at 75oC for 90 minutes, was studied.
The results indicated that it is possible to produce lightweight cement mortar, using any type of aggregates mentioned above, with compressive strength satisfying the requirements of clay brick class C of Iraqi Standard, that used in partitions, for a mix proportion of 1:1, except when using chopped rubber tires that need using mix proportion of 1:0.5 to satisfy the strength requirements, where the use of this aggregate type needs higher w/c ratio and superplasticizer content to get the required flow, which leads to lower strength in comparison with the other types. As for chopped plastic aggregate, although it needs lower water and superplasticizer content to get the required flow and strength, care should be taken to balance betweenthe amount of waterand superplasticizer addedto avoidthe possibility of segregation in it. So it was found that using the mixture of chopped plastic and rubber aggregate give the best properties.
Results also indicated that using all aggregate typeswith cement: aggregate mix proportion 1:1 satisfy the flexural strength requirements of American Standards for cellulosic fiber insulating boards, and were with thermal conductivity valueslower than that for brick and concrete having density lower than 2000 kg/m3. The results indicated that partial replacement of 10% mixed waste aggregates by normal sand cause increase in strength but in the same time increase density and thermal conductivity for the produced mortar.
Results also indicated that curing by autoclave or curing with 50% or 100% CO2 cause increase in the 7 days strength compared with those cured by water but they show almost the same strength at 28 days age.

Pozzolanic Activity and Compressive Strength of Concrete Incorporated nano/micro Silica

Maan S. Hassan; Shakir A. Salih; Mohammed S.Nasr

Engineering and Technology Journal, 2016, Volume 34, Issue 3, Pages 483-496

This paper aims to give a recommendation about the suitable nano silica proportion and curing method for testing its strength pozzolonic activity, in addition to suggest a mixing or batching procedure of this material with other concrete ingredients. Theinfluence of nanoand micro silicaon concrete compressive strength is also studied. Three proportions of nano silica (0.5, 5, &10%) , two curing methods (accelerated in oven and normal in water) and two tested agesare used in pozzolonic activity test of nano silica. For compressive strength test, eleven mixes are considered:without-adding (two mixes), three micro silica (M) mixes with replacement ratios of 5, 10 & 15%, four nano silica (N) mixeswith replacement ratiosof 0.5,1.5, 3 & 5%, and three micro plus nano silica mixes (0.5N+9.5M,1.5N+8.5M and 3N+7M%) are adopted.Results of pozzolanic activity test denoted that nano silica has remarkable pozzolanic activity for all tested replacements.However, it is suggest using 5% nano silica for performing this testby usingeither accelerated or water curing. Additionally, it was found that nano silica had more impact on compressive strength of concrete than micro silica for all tested ages.Where, maximum enhancement ratios of compressive strength were about 33% and 27% for 3% nano silica mix at 7 and 90 days age respectively, and 22% for 5% nano silica mix at 28 days age. For micro silica mixes, higher improvement ratios were found in 15% micro silica mix: 2%,5%&7% at 7,28 &90 days age respectively.

Mechanical Properties of High Strength Concrete Containing Different Cementitious Materials

Hisham K. Ahmed; Oday A. Abd

Engineering and Technology Journal, 2016, Volume 34, Issue 1, Pages 96-110

High strength concrete hasstrength significantly beyond what is used in normal practice. According to American Concrete Institute (ACI), high strength concrete revised the definition to cover mixtures with specified design strength of 55 MPa or more.
The main objective of this investigation isto study the effect of using different supplementary cementitious materials in binary blends on mechanical properties of high strength concrete.
The experimental work includes threestages: firstly, preparation of cementitious materials (metakaolin and pumice) from local materials,second involves conducting several trial mixes to choose the best of superplasticizer that satisfies the required properties and to specify the optimum water content which is designed in laboratory by 0.3 W/Cm ratio, to achieve workability with (60-80mm) slump and the best compressive strength which was 64.6 at 28 days.
Thirdly carrying out tests to find out the compressive strength, splitting tensile strength, modulus of rupture, on binary concretes including mixes containing silica fume as cement replacement at percentages of 8%, 10% and 15%, mixes containing metakaolin as cement replacement levels of 10%, 15%, and20% and mixes containing pumice at cement replacement of 10%, 15%, and 20%.These properieswere measured at ages ranging from7days to 180 days.
The resultsindicate that the silica fume performs better than other supplementary cementitious materials(metakaolin or pumice) in terms of the compressive strength, splitting tensile strength and modulus of rupture development at ages of 7,28,60,90and180 days where the average percentage of increase when using 8%,10% and 15% ofsilica fume was about(19%,23% and 18.7%) ,respectively, while when using 10%,15% and 20%metakaolin the average percentage of increase was (10%,12.6% and 4%) respectively, also when using 10%,15% and 20% of pumice the average percentage of increase was (2.6%, 6% and 1.5%), respectively.

Influence of Incorporating Construction Building Demolition as Recycled Aggregate on Concrete Behavior

Shatha Sadiq Hussen

Engineering and Technology Journal, 2016, Volume 34, Issue 1, Pages 33-49

Because of increasing waste production and public concerns about the environment, it is desirable to recycle materials from construction and building demolition. This study aimed to find a technique for producing recycled aggregate concrete obtained from construction and building demolition waste. Laboratory trials were conducted to investigate the possibility of using recycled aggregate from different sources in Iraq, as a partial replacement of both coarse and fine natural aggregates or one of them. Recycled aggregate consists of crushed concrete (CC) or acombination of crushed brick (CB) and crushed concrete (CC). The aggregate in concrete was replaced with 10%, 20%, 30% and 50% by weight of crushedconcrete (CC) or crushed brick (CB) and crushed concrete CC. Some of mechanical properties of recycled aggregate concrete as compared to those of conventional normal aggregate concrete are studied. Compressive strength and the splitting tensile strength were determined after curing for 7, 28, and 90 days while density was determined after28 days.From these results, it is reasonable to assume that the use of recycled concrete aggregate does not jeopardize the mechanical properties of concretefor replacement ratios up to 50%. The concrete prepared with the crushed concrete only as a partial replacement of natural aggregate achieved the highest strength values at 7, 28and 90 days. The results suggested that an aggregate that contains 50% recycled aggregate is optimum for producing recycled aggregate concrete The test results showed that the replacement of coarse or fine natural aggregate by recycled brick aggregate at the levels of 10,20,30 and 50% had little effect on the compressive strength of the specimens.

Thermal Properties of Recycle Aggregate Concrete with Different Densities

Amer M. Ibrahim; Shakir A. Al-Mishhadani; Noor Al Huda H. Ahmed

Engineering and Technology Journal, 2015, Volume 33, Issue 9, Pages 2027-2038

The present research intended to determine thermal properties (thermal
conductivity, thermal diffusivity and specific heat) of concrete manufactured by recycle waste of clay brick and thermostone for using it as aggregate after crushing process. For this purpose, three concrete mixes were prepared one of them using crushed clay brick as aggregate and two others were used crushed thermostone as aggregate too, these three mixes compared with reference normal concrete mix.
Specific heat was measured by using semi-adiabatic calorimeter method whereas thermal diffusivity was measured by using heating-cooling system. Thermal conductivity was obtained by multiplying the thermal diffusivity, specific heat and density. From experimental laboratory work, it was concluded that the thermal diffusivity increase with concrete density increment, but the specific heat was decreased with concrete density increment. Thermal conductivity had a linear relationship with thermal diffusivity. Mixing ratio also had an influence on thermal properties of concrete.

New Technique for Producing Vacuum Concrete

Haitham Hazim Saeed; Anas Amjed Ezzulddin

Engineering and Technology Journal, 2015, Volume 33, Issue 3, Pages 659-667

In this work a new technique is used to produce vacuum dewatered concrete. In this technique perforated PVC pipes encased in cotton cloth are used to dewater concrete from inside of concrete volume, rather than from the surface, as is the case in the conventional vacuum dewatering method. These pipes are laid in position inside concrete forms, and a vacuum pump is connected to the dewatering pipes, which is operated after casting of fresh concrete to remove the excessive water from internal portion. Properties of vacuum dewatered concrete using the new technique are investigated by a series of tests such as compressiveand flexural strength tests. Based on test results, the new technique improves concrete strength and other mechanical properties particularly at early ages. The new dewatering technique is a good alternative to the conventional vacuum dewatering technique and can have a wider range of practical applications than the conventional method.

Effect of Practical Curing Methods on the Properties of Roller Compacted Concrete

Hisham K. Ahmed; Intesar Kadhim Gata

Engineering and Technology Journal, 2015, Volume 33, Issue 2, Pages 500-511

Roller Compacted Concrete (RCC) is a technology characterized mainly by the use of rollers for compaction. This construction method permits considerable reduction in costs and construction time of dams and roads. It is necessary to study the curing of RCC especially in hot weather because RCC has no slump and has low W/C ratio. Therefore the primary scope of this research is to study the effect of various curing methods (continuous watering, wet burlap, nylon, sprinkling, curing cycles, and curing compound) after 24 hrs from casting on the physical properties of roller compacted concrete.
The mix proportion which was used in this investigation, was designed and laboratory tried on the basis of using 250 kg/m³ of Ordinary Portland Cement. This work involves preparing cylindrical specimens with (diameter of 150 mm and height of 300 mm) for measuring the compressive strength, splitting-tensile strength, and static modulus of elasticity. And it also includes prism specimens with (100×100×400 mm) for measuring the modulus of rupture (flexural strength).
Results show that the curing of RCC with continuous watering clearly improved the RCC properties. The results also indicate that the RCC specimens without curing (left in air) suffered from permanent loss of strengths ranging between 20 to 25 % when compared with continuous watering at age of 28 days.

Effect of Compaction Methods on the Properties of Roller Compacted Concrete

Hisham Khalid Ahmed; Azal Thair Abdulrazzak

Engineering and Technology Journal, 2014, Volume 32, Issue 10, Pages 2454-2464

Roller compacted concrete (RCC) is a technology characterized mainly use of roller for compaction. This construction method permits considerable reduction in costs and construction time of dams and roads. The main aim of this work is to investigate the influence of compaction methods on the properties of RCC. the experimental program included preparing cylindrical specimens with (diameter of 150 mm by height of 300 mm) for measuring the compressive strength, splitting tensile strength and absorption. And it also includes prism specimens with (100*100*400) mm for measuring the modulus of rupture. These specimens were compacted by using different compaction methods, dynamicly (modified proctor hammer compaction (CBR test), vibrator table, and vibrator table with CBR test) and statically (compacting pressure (compacting pressure 10 MPa, 15 MPa and 20 MPa).
Results show that the compaction methods have a noticeable effect on the properties of RCC. The results also indicated that using vibrator table with CBR show an increase in the compressive strength, splitting tensile strength and modulus of rupture by 23%, 14% and 13%, respectively as compared with compacted by vibrator table only. The results also show that using compacting pressure 20 MPa show an increase in the compressive strength, splitting tensile strength and modulus of rupture by 31%, 27%, and 39%, respectively as compared with that made by compacting pressure 10 MPa.

Effect of Concrete Compressive Strength and Compression Reinforcement in Compression Zone on the Ductility of Reinforced Concrete Beams

Sawsan Akram Hassan; Awadh Ewayed Ajeel

Engineering and Technology Journal, 2014, Volume 32, Issue 5, Pages 1106-1116

Ductility is a mechanical property used to describe the extent to which materials can be deformed plastically without fracture giving warning of impending failure. In this paper the effect of increasing the strength in the compression zone of reinforced concrete beams on ductility was investigated. Seven reinforced concrete beams were tested for this purpose. The tested beams were divided into two groups depending on the manner at which the strength of the compression zone was increased. In the first group, the increase was done by increasing the amount of compression reinforcement. Four ratios of compression reinforcement were adopted. In the second group, the increase in the strength of the compression zone was done by increasing the concrete compressive strength in the upper third of the cross section which was subjected to compression stresses. Four compressive strengths were adopted .One beam was used as reference for the two groups. It was found that, the compression zone strengthening, by the two manners, increases both strength and ductility of the beams; but the increases due to increase the ratio of compressive reinforcement is higher and more safety than that attained due to increasing concrete compressive strength.

One Parameter Composite Semigroups of Linear Bounded Operators in Strong Operator Topology of Schatten Class Cp

Samir Kasim Hassan; Al-Taie M; Al-Malki Anam; Al-Attar Abeer; Mustafa Khaleel Ismael; Fatema Ahmed Sadeq; Radhi A .Zboon; Jehad R.Kider; Samir K .Hassan; Hussain J. M. Alalkawi; Raad H. Majid; Rawaa A. Alomairy; Luma Abdul Ghani Zghair; Hadia Kadhim J.Al-Ogili; Assifa M. Mohamad; Abbas Sheyaa Alwan; Haider L. Aneed; Assim H Yousif; Salema Sultan Salman; Abbas Hussien Miry; Abduladhem A.Ali; Mohammed Zeki Al-Faiz; Sabah N. mahmood; Khansaa Dawood Selman; Shaymaa Tareq Kadhim

Engineering and Technology Journal, 2011, Volume 29, Issue 8, Pages 1463-1470

For semigroups of linear bounded operators on Hilbert spaces, the problem of
being in Cp , 0 Keywords

Behavior of Plain and High Performance Polypropylene Fiber Concrete Subjected to Elevated Temperatures

Luma Abdul Ghani Zghair

Engineering and Technology Journal, 2011, Volume 29, Issue 8, Pages 1517-1535

The aim of this work is to determine the residual compressive strength and splitting tensile strength after exposure to an elevated temperature (between100 to 500 C ◌ْ ) of plain and polypropylene fiber reinforced concrete (PPFRC) in comparison with specimens exposed to ordinary temperature 25C ◌ْ . High – performance concrete mixes were produced by using high rang reducing agent superplasticizer (SP) and 10% high reactivity metakaoline (HRM) as a partial replacement by weight of cement (350)Kg/m3 . A single concrete mix with HRM,
SP and four PPF contents of (0.25, o.5, o.75 and 1%) by volume were adopted. The workability of the concrete was kept constant ( slump 100 ± 5mm ).Each group of specimens ( plain and PPFRC ) was heated to a specified temperature and kept at the temperature for one hour before being gradually cooled to room temperature and then they were tested .
The results show at ordinary temperatures 25 C ◌ْ, the addition of fiber volume fraction (VF%) of (0.25%) increases the compressive ( 20.6% ) comparable to HPC without fiber . While the addition of ( 0.5 , 0.75 and 1% ) of polymer fibers , the compressive strength decreased (12.6 , 19 and 33%) respectively comparable to HPC without fiber . On the other hand the addition of (VF%) of (0.25) increased splitting tensile strength ( 15%) comparable to HPC without fiber . while the
addition of fiber volume fraction (VF%) of (0.5 ) increased splitting tensile strength by a percentage which is lower than that in specimens with VF% of 0.25 , the increase in splitting tensile strength was ( 6%) comparable to HPC without fiber at ordinary temperatures
The results also shows that , when (1% ) fibers was used , the splitting tensile strength decreased ( 10.8%) in comparable to HPC without fiber At elevated temperature the results show an appreciable decrease in compressive strength and splitting tensile strength after exposure to temperature higher than 300 C ◌ْ of both plain and PPFRC
Specimens containing PPF ( 0.25 , 0.5 , and 0.75 %) the percentage of
reduction in splitting tensile strength is lower than that in HPC specimens ( without fibers ) after exposure to a temperature ( 500 ,300 and 100 C ◌ْ ) comparable to normal temperature 25C ◌ْ .While specimen containing PPF ( 1% ) the percentage of reduction in splitting tensile strength was higher than specimen without PPF after exposure to a similar temperature .On the other hand , specimens containing PPF ( 0.25 , 0.5 , 0.75 and 1 %) the percentage of reduction in compressive strength is higher than that in HPC specimens ( without fibers ) after exposure to a temperature (500 ,300 and 100 C ◌ْ). comparable to normal temperature 25C ◌ْ

Mechanical Strength of Silicon Carbide Bonded with Iraqi Clays

Abdul Mutalb Al Sheikh; Shihab Ahmed Zaidan Al- Juboori; Kassim S. Kassim

Engineering and Technology Journal, 2011, Volume 29, Issue 4, Pages 665-676

Two types of Iraqi clays (Kaolin and Bentonite) were used in bonding process
with different weight percentage (5%, 10%, 15%, 20%, and 25%) and with
different particle size from clays and silicon carbide.
The specimens were formed by using low biaxial pressing and two types of
internal lubricants (sodium silicate and the carbon paste) to increase the
specimen's cohesion. These specimens were sintered at various temperatures of
(1100°C, 1200°C, 1300°C, and 1400°C).
Increasing of clay percentage leads to decreasing the porosity. But it leads to
increase mechanical properties (compressive strength, diametrical strength and
bending strength ). Also, the effect of particle size on all properties is studied
together with sintering temperature. All mechanical properties (when bonded SiC
with bentonite) are higher than kaolin bonded SiC.

Mechanical Properties of High-Strength Fiber Reinforced Concrete

Zaid Muhammad Kani Al-Azzawi; Kaiss Sarsam

Engineering and Technology Journal, 2010, Volume 28, Issue 12, Pages 2442-2453

Experimental results of this work in addition to a wide range of data from previous work
were analyzed to study the mechanical properties and strength of high-strength concrete with and
without fibers. Different types of steel fibers (straight, hooked, duoform, crimped) with a volume
fraction ranging from 0 to 2 percent were studied. The concrete compressive strength ranged from 41
to 115 MPa. The influence of fiber on the compressive strength, axial strain, modulus of elasticity,
Poisson's ratio, modulus of rupture, and splitting tensile strength, were studied. In addition to that,
size effect of control specimens on high-strength fiber reinforced concrete materials, was observed.
The main conclusion indicates that high-strength concrete (HSC) properties, especially with fibers
are significantly different from normal-strength concrete (NSC).

The Production of Self-Compacting Concrete with Normal Cement Content

Luma A. G. Al- Rawi; Tariq S. Al-Attar; Shakir A. Al-Mishhadani

Engineering and Technology Journal, 2009, Volume 27, Issue 2, Pages 310-320

The main object of this work is to evaluate the possibility for using reasonable cement
content and fine materials to reduce costs of expensive chemical admixtures needed for the
manufacturing of self-compacting concrete (SCC). In this work, three values of cement content
are used (rich, medium and lean mixes) with cement content of 400, 300 and 250 kg/m3
respectively . Two maximum aggregate sizes of (10 and 20mm) for each cement content are
used. The powder content material is (cementations + filler ) is maintained constant (500kg/m3)
while the W/cm ratio ranges from 0.43 to 0.68. 10% Reactive Metakaolin Class N is used as a
partial replacement by weight of cement. On the other hand, limestone dust was used as a
partial replacement by weight of the powder content Tests were carried out on all mixes to
obtain the properties of fresh concrete in terms of viscosity and stability. The results showed that
increasing the percentage of filler (limestone dust) from 20% in rich mixes to50% in lean mixes
of the total weight of the powder content reduces the amount of cement in SCC without
significant effect on the fresh properties of the SCC mixes. This conclusion is significant from
the economical point of view. The mechanical properties of hardened SCC mixes are also
assessed. (compressive strength, modulus of elasticity ). The results obtained from this work
show that it is possible to produce SCC with different levels of cement content (250 to400kg/m3)
using local available materials which satisfy the requirements of this type of concrete .The test
data collected indicate that these materials can be used in the manufacturing of economical SCC.