Abstract: Due to their fluidity and simplicity of use, self-compacting concretes (SCCs) have undeniable advantages. In recent years, the role of metakaolin as a one of pozzolanic materials in concrete has been considered by researchers. It can modify various properties of concrete, due to high pozzolanic reactions and also makes a denser microstructure. The objective of this paper is to examine the influence of three type of Portland cement and metakaolin on fresh state, compressive strength and sulfuric acid attacks in self- consolidating concrete at early age up to 90 days of curing in lime water. Six concrete mixtures were prepared with three types of different cement as Portland cement type II, Portland Slag Cement (PSC), Pozzolanic Portland Cement (PPC) and 15% substitution of metakaolin by every cement. The results show that the metakaolin admixture increases the viscosity and the demand amount of superplasticizer. According to the compressive strength results, the highest value of compressive strength was achieved for PSC and without any metakaolin at age of 90 days. Conversely, the lowest level of compressive strength at all ages of conservation was obtained for PPC and containing 15% metakaolin. According to this study, the total substitution of PSC and PPC by Portland cement type II is beneficial to the increasing in the chemical resistance of the SCC with respect to the sulfuric acid attack. On the other hand, this increase is more noticeable by the use of 15% of metakaolin. Therefore, it can be concluded that metakaolin has a positive effect on the chemical resistance of SCC containing of Portland cement type II, PSC, and PPC.
Abstract: The aim of this study is to conduct an experimental investigation on the influence of complete replacement of natural coarse aggregate with spherically-shape and crushed waste cathode ray tube (CRT) glass to the aspect of workability, density, and compressive strength of the concrete. After characterizing the glass, a group of concrete mixes was prepared to contain a 40% spherical CRT glass and 60% crushed CRT glass as a complete (100%) replacement of natural coarse aggregates. From a total of 16 types of concrete mixes, the optimum proportion was selected based on its best performance. The test results showed that the use of spherical and crushed glass that possesses a smooth surface, rounded, irregular and elongated shape, and low water absorption affects the workability of concrete. Due to a higher specific gravity of crushed glass, concrete mixes containing CRT glass had a higher density compared to ordinary concrete. Despite the spherical and crushed CRT glass being stronger than gravel, the results revealed a reduction in compressive strength of the concrete. However, using a lower water to binder (w/b) ratio and a higher superplasticizer (SP) dosage, it is found to enhance the compressive strength of 60.97 MPa at 28 days that is lower by 13% than the control specimen. These findings indicate that waste CRT glass in the form of spherical and crushed could be used as an alternative of coarse aggregate that may pave the way for the disposal of hazardous e-waste.
Abstract: To obtain the high quality and essential workability of mortar, different types of superplasticizers are used. The superplasticizers are the chemical admixture used in the mix to improve the fluidity of mortar. Many factors influenced the superplasticizer to disperse the cement particle in the mortar. Nature and amount of replaced cement by slag, mixing procedure, delayed addition time, and heat stimulation technique of superplasticizer cause the varied effect on the fluidity of the cementitious material. In this experiment, the superplasticizers were heated for 1 hour under 60 °C in a thermostatic chamber. Furthermore, the effect of delayed addition time of heat stimulated superplasticizers (SP) was also analyzed. This method was applied to two types of polycarboxylic acid based ether SP (precast type superplasticizer (SP2) and ready-mix type superplasticizer (SP1)) in combination with a partial replacement of normal Portland cement with blast furnace slag (BFS) with 30% w/c ratio. On the other hands, the fluidity, air content, fresh density, and compressive strength for 7 and 28 days were studied. The results indicate that the addition time and heat stimulation technique improved the flow and air content, decreased the density, and slightly decreased the compressive strength of mortar. Moreover, the slag improved the flow of mortar by increasing the amount of slag, and the effect of external temperature of SP on the flow of mortar was decreased. In comparison, the flow of mortar was improved on 5-minute delay for both kinds of SP, but SP1 has improved the flow in all conditions. Most importantly, the transition points in both types of SP appear to be the same, at about 5±1 min. In addition, the optimum addition time of SP to mortar should be in this period.
Abstract: The stock market can provide huge profits in a relatively short time in financial sector; however, it also has a high risk for investors and traders if they are not careful to look the factors that affect the stock market. Therefore, they should give attention to the dynamic fluctuations and movements of the stock market to optimize profits from their investment. In this paper, we present a nonlinear autoregressive exogenous model (NARX) to predict the movements of stock market; especially, the movements of the closing price index. As case study, we consider to predict the movement of the closing price in Indonesia composite index (IHSG) and choose the best structures of NARX for IHSG’s prediction.
Abstract: The workability of hybrid alkaline cements is a field of knowledge that still needs further research efforts. This paper reports experimental results of 32 hybrid cement mixes regarding the joint effect of sodium hydroxide concentration, the use of a commercial superplasticizer and a biopolymer on the flow and compressive strength performance. The results show that the use of commercial admixtures led to a slightly increase in the flow of mortars with lower sodium hydroxide concentration.
Abstract: In this paper, an experimental investigation on the effect of Isfahan Ground Granulate Blast Furnace Slag (GGBS) on the compressive strength development of self-consolidating concrete (SCC) and normal concrete (NC) was performed. For this purpose, Portland cement type I was replaced with GGBS in various Portions. For NC and SCC Mixes, 10*10*10 cubic cm specimens were tested in 7, 28 and 91 days. It must be stated that in this research water to cement ratio was 0.44, cement used in cubic meter was 418 Kg/m³ and Superplasticizer (SP) Type III used in SCC based on Poly-Carboxylic acid. The results of experiments have shown that increasing GGBS Percentages in both types of concrete reduce Compressive strength in early ages.
Abstract: Lignin is a molecule derived from wood and also generated as waste from the paper industry. With a view to its valorization and protection of the environment, we are interested in its use as a superplasticizer-type adjuvant in mortars and concretes to improve their mechanical strengths. The additives of the concrete have a very strong influence on the properties of the fresh and / or hardened concrete. This study examines the development and use of industrial waste and lignin extracted from a renewable natural source (wood) in cementitious materials. The use of these resources is known at present as a definite resurgence of interest in the development of building materials. Physicomechanical characteristics of mortars are determined by optimization quantity of the natural superplasticizer. The results show that the mechanical strengths of mortars based on natural adjuvant have improved by 20% (64 MPa) for a W/C ratio = 0.4, and the amount of natural adjuvant of dry extract needed is 40 times smaller than commercial adjuvant. This study has a scientific impact (improving the performance of the mortar with an increase in compactness and reduction of the quantity of water), ecological use of the lignin waste generated by the paper industry) and economic reduction of the cost price necessary to elaboration of self-compacting mortars and concretes).
Abstract: The aim of this article is to access the optimal mix design of self-compacting light weight concrete. The effects of magnetic water, superplasticizer based on polycarboxylic-ether, and silica fume on characteristics of this type of concrete are studied. The workability of fresh concrete and the compressive strength of hardened concrete are considered here. For this purpose, nine mix designs were studied. The percentages of superplasticizer were 0.5, 1, and 2% of the weight of cement, and the percentages of silica fume were 0, 6, and 10% of the weight of cement. The water to cementitious ratios were 0.28, 0.32, and 0.36. The workability of concrete samples was analyzed by the devices such as slump flow, V-funnel, L box, U box, and Urimet with J ring. Then, the compressive strengths of the mixes at the ages of 3, 7, 28, and 90 days were obtained. The results show that by using magnetic water, the compressive strengths are improved at all the ages. In the concrete samples with ordinary water, more superplasticizer dosages were needed. Moreover, the combination of superplasticizer and magnetic water had positive effects on the mixes containing silica fume and they could flow easily.
Abstract: This paper reports the strength and durability properties of high strength high performance concrete incorporating rice husk ash (RHA) having high silica, low carbon content and appropriate fineness. In this study concrete containing 10%, 15% and 20% RHA as cement replacement and water to binder ratio of 0.25 were investigated. The results show that increasing amount of RHA increases the dosage of superplasticizer to maintain similar workability. Partial replacement of cement with RHA did not increase the early age compressive strength of concrete. However, concrete containing RHA showed higher compressive strength at later ages. The results showed that compressive strength of concrete in the 90-115 MPa range can be obtained at 28 curing days and the durability properties of RHA concrete performed better than that of control concrete. The water absorption of concrete incorporating 15% RHA exhibited the lowest value. The porosity of concrete is consistent with water absorption whereby higher replacement of RHA decreased the porosity of concrete. There is a positive correlation between reducing porosity and increasing compressive strength of high strength high performance concrete. The results also indicate that up to 20% of RHA incorporation could be advantageously blended with cement without adversely affecting the strength and durability properties of concrete.
Abstract: Geopolymer (cement-free) concrete is the most promising green alternative to ordinary Portland cement concrete and other cementitious materials. While a range of different geopolymer concretes have been produced, a common feature of these concretes is heat curing treatment which is essential in order to provide sufficient mechanical properties in the early age. However, there are several practical issues with the application of heat curing in large-scale structures. The purpose of this study is to develop cement-free concrete without heat curing treatment. Experimental investigations were carried out in two phases. In the first phase (Phase A), the optimum content of water, polycarboxylate based superplasticizer contents and potassium silicate activator in the mix was determined. In the second stage (Phase B), the effect of ground granulated blast furnace slag (GGBFS) incorporation on the compressive strength of fly ash (FA) and Slag based geopolymer mixtures was evaluated. Setting time and workability were also conducted alongside with compressive tests. The results showed that as the slag content was increased the setting time was reduced while the compressive strength was improved. The obtained compressive strength was in the range of 40-50 MPa for 50% slag replacement mixtures. Furthermore, the results indicated that increment of water and superplasticizer content resulted to retarding of the setting time and slight reduction of the compressive strength. The compressive strength of the examined mixes was considerably increased as potassium silicate content was increased.
Abstract: Fresh concrete has one of dynamic properties known
as slump. Slump of concrete is design to compatible with placing
method. Due to hydration reaction of cement, the slump of concrete
is loss through time. Therefore, delayed concrete probably get reject
because slump is unacceptable. In order to recover the slump of
delayed concrete the second dose of superplasticizer (naphthalene
based type F) is added into the system, the slump recovery can be
done as long as the concrete is not setting. By adding superplasticizer
as solution for recover unusable slump loss concrete may affects
other concrete properties. Therefore, this paper was observed setting
times and compressive strength of concrete after being re-dose with
chemical admixture type F (superplasticizer, naphthalene based) for
slump recovery. The concrete used in this study was fly ash concrete
with fly ash replacement of 0%, 30% and 50% respectively. Concrete
mix designed for test specimen was prepared with paste content (ratio
of volume of cement to volume of void in the aggregate) of 1.2 and
1.3, water-to-binder ratio (w/b) range of 0.3 to 0.58, initial dose of
superplasticizer (SP) range from 0.5 to 1.6%. The setting times of
concrete were tested both before and after re-dosed with different
amount of second dose and time of dosing. The research was
concluded that addition of second dose of superplasticizer would
increase both initial and final setting times accordingly to dosage of
addition. As for fly ash concrete, the prolongation effect was higher
as the replacement of fly ash increase. The prolongation effect can
reach up to maximum about 4 hours. In case of compressive strength,
the re-dosed concrete has strength fluctuation within acceptable range
of ±10%.
Abstract: This paper aimed to introduce the solution of concrete
slump recovery using chemical admixture type-F (superplasticizer,
naphthalene base) to the practice in order to solve unusable concrete
problem due to concrete loss its slump, especially for those tropical
countries that have faster slump loss rate. In the other hand, randomly
adding superplasticizer into concrete can cause concrete to segregate.
Therefore, this paper also develops the estimation model used to
calculate amount of second dose of superplasticizer need for concrete
slump recovery. Fresh properties of ordinary Portland cement
concrete with volumetric ratio of paste to void between aggregate
(paste content) of 1.1-1.3 with water-cement ratio zone of 0.30 to
0.67 and initial superplasticizer (naphthalene base) of 0.25%-1.6%
were tested for initial slump and slump loss for every 30 minutes for
one and half hour by slump cone test. Those concretes with slump
loss range from 10% to 90% were re-dosed and successfully
recovered back to its initial slump. Slump after re-dosed was tested
by slump cone test. From the result, it has been concluded that, slump
loss was slower for those mix with high initial dose of
superplasticizer due to addition of superplasticizer will disturb
cement hydration. The required second dose of superplasticizer was
affected by two major parameters, which were water-cement ratio
and paste content, where lower water-cement ratio and paste content
cause an increase in require second dose of superplasticizer. The
amount of second dose of superplasticizer is higher as the solid
content within the system is increase, solid can be either from cement
particles or aggregate. The data was analyzed to form an equation use
to estimate the amount of second dosage requirement of
superplasticizer to recovery slump to its original.
Abstract: This paper presents results of compressive strength,
capillary water absorption, and density tests conducted on concrete
containing recycled aggregate (RCA) which is obtained from
structural waste generated by the construction industry in Turkey. In
the experiments, 0%, 15%, 30%, 45% and 60% of the normal
(natural) coarse aggregate was replaced by the recycled aggregate.
Maximum aggregate particle sizes were selected as 16 mm, 22,4 mm
and 31,5 mm; and 0,06%, 0,13% and 0,20% of air-entraining agent
(AEA) were used in mixtures. Fly ash and superplasticizer were used
as a mineral and chemical admixture, respectively. The same type
(CEM I 42.5) and constant dosage of cement were used in the study.
Water/cement ratio was kept constant as 0.53 for all mixture. It was
concluded that capillary water absorption, compressive strength, and
density of concrete decreased with increasing RCA ratio. Increasing
in maximum aggregate particle size and amount of AEA also affect
the properties of concrete significantly.
Abstract: White concrete facade elements are widely used in
construction industry. It is challenging to achieve the desired
workability in casting of white concrete elements. Particle Matrix
model was used for proportioning the self-compacting white concrete
(SCWC) to control segregation and bleeding and to improve
workability. The paper presents how to reach the target slump flow
while controlling bleeding and segregation in SCWC. The amount of
aggregates, binders and mixing water, as well as type and dosage of
superplasticizer (SP) to be used are the major factors influencing the
properties of SCWC. Slump flow and compressive strength tests were
carried out to examine the performance of SCWC, and the results
indicate that the particle matrix model could produce successfully
SCWC controlling segregation and bleeding.
Abstract: Self-compacting concrete (SCC) developed in Japan
in the late 80s has enabled the construction industry to reduce
demand on the resources, improve the work condition and also
reduce the impact of environment by elimination of the need for
compaction. Fuzzy logic (FL) approaches has recently been used to
model some of the human activities in many areas of civil
engineering applications. Especially from these systems in the model
experimental studies, very good results have been obtained. In the
present study, a model for predicting compressive strength of SCC
containing various proportions of fly ash, as partial replacement of
cement has been developed by using Fuzzy Inference System (FIS).
For the purpose of building this model, a database of experimental
data were gathered from the literature and used for training and
testing the model. The used data as the inputs of fuzzy logic models
are arranged in a format of five parameters that cover the total binder
content, fly ash replacement percentage, water content,
superplasticizer and age of specimens. The training and testing results
in the fuzzy logic model have shown a strong potential for predicting
the compressive strength of SCC containing fly ash in the considered
range.
Abstract: This work is focused on the study of valuation of
recycled concrete aggregates, by measuring certain properties of
concrete in the fresh and hardened state. In this study, rheological
tests and physic-mechanical characterization on concretes and
mortars were conducted with recycled concrete whose geometric
properties were identified aggregates. Mortars were elaborated with
recycled fine aggregate (0/5mm) and concretes were manufactured
using recycled coarse aggregates (5/12.5 mm and 12.5/20 mm). First,
a study of the mortars was conducted to determine the effectiveness
of polycarboxylate superplasticizer on the workability of these and
their action deflocculating of the recycled sand. The rheological
behavior of mortars based on fine aggregate recycled was
characterized. The results confirm that the mortars composed of
different fractions of recycled sand (0 /5) have a better mechanical
properties (compressive and flexural strength) compared to normal
mortar. Also, the mechanical strengths of concretes made with
recycled aggregates (5/12.5 mm and 12.5/20 mm), are comparable to
those of conventional concrete with conventional aggregates,
provided that the implementation can be improved by the addition of
a superplasticizer.
Abstract: Cement-based grouts has been used successfully to
repair cracks in many concrete structures such as bridges, tunnels,
buildings and to consolidate soils or rock foundations. In the present
study the rheological characterization of cement grout with
water/binder ratio (W/B) is fixed at 0.5. The effect of the replacement
of cement by bentonite (2 to 10% wt) in presence of superplasticizer
(0.5% wt) was investigated. Several rheological tests were carried out
by using controlled-stress rheometer equipped with vane geometry in
temperature of 20°C. To highlight the influence of bentonite and
superplasticizer on the rheological behavior of grout cement, various
flow tests in a range of shear rate from 0 to 200 s-1 were observed.
Cement grout showed a non-Newtonian viscosity behavior at all
concentrations of bentonite. Three parameter model Herschel-
Bulkley was chosen for fitting of experimental data. Based on the
values of correlation coefficients of the estimated parameters, The
Herschel-Bulkley law model well described the rheological behavior
of the grouts. Test results showed that the dosage of bentonite
increases the viscosity and yield stress of the system and introduces
more thixotropy. While the addition of both bentonite and
superplasticizer with cement grout improve significantly the fluidity
and reduced the yield stress due to the action of dispersion of SP.
Abstract: Self-Consolidating Concrete (SCC) is considered as a relatively new technology created as an effective solution to problems associated with low quality consolidation. A SCC mix is defined as successful if it flows freely and cohesively without the intervention of mechanical compaction. The construction industry is showing high tendency to use SCC in many contemporary projects to benefit from the various advantages offered by this technology.
At this point, a main question is raised regarding the effect of enhanced fluidity of SCC on the structural behavior of high strength self-consolidating reinforced concrete.
A three phase research program was conducted at the American University of Beirut (AUB) to address this concern. The first two phases consisted of comparative studies conducted on concrete and mortar mixes prepared with second generation Sulphonated Naphtalene-based superplasticizer (SNF) or third generation Polycarboxylate Ethers-based superplasticizer (PCE). The third phase of the research program investigates and compares the structural performance of high strength reinforced concrete beam specimens prepared with two different generations of superplasticizers that formed the unique variable between the concrete mixes. The beams were designed to test and exhibit flexure, shear, or bond splitting failure.
The outcomes of the experimental work revealed comparable resistance of beam specimens cast using self-compacting concrete and conventional vibrated concrete. The dissimilarities in the experimental values between the SCC and the control VC beams were minimal, leading to a conclusion, that the high consistency of SCC has little effect on the flexural, shear and bond strengths of concrete members.
Abstract: Compatibility between sulfonated acetone- formalehyde superplasticizer (SAF) and copolymer-based grinding aids (GA) were studied by fluidity, Zeta potential, setting time of cement pasts, initial slump and slump flow of concrete and compressive strength of concrete. ESEM, MIP, and XRD were used to investigate the changing of microstructure of interior concrete. The results indicated that GA could noticeably enhance the dispersion ability of SAF. It was found that better fluidity and slump-keeping ability of cement paste were obtained in the case of GA. In addition, GA together with SAF had a certain retardation effect on hydration of cement paste. With increasing of the GA dosage, the dispersion ability and retardation effect of admixture increased. The compressive strength of the sample made with SAF and GA after 28 days was higher than that of the control sample made only with SAF. The initial slump and slump flow of concrete increased by 10.0% and 22.9%, respectively, while 0.09 wt.% GA was used. XRD examination indicated that new products were not found in the case of GA. In addition, more dense arrangement of hydrates and lower porosity of the specimen were observed by ESEM and MIP, which contributed to higher compressive strength.
Abstract: In the modern construction practices, industrial wastes
or by-products are largely used as raw materials in cement and
concrete. These impart many benefits to the environment and bringabout
an economic impact because the cost of waste disposal is
constantly increasing due to strict environmental regulations. It was
reported in literature that the leakage of oil onto concrete element in
older cement grinding unit resulted in concrete with greater resistance
to freezing and thawing. This effect was thought to be similar to
adding an air-entraining chemical admixture to concrete. This paper
presents an investigation on the load deflection behaviour and crack
patterns of reinforced concrete (RC) beams subjected to four point
loading. Ten 120x260x1900 mm beams were cast with 100%
ordinary Portland cement (OPC) concrete, 20% fly ash (FA) and 20%
rice husk ash (RHA) blended cement concrete. 0.15% dosage of
admixtures (used engine oil, new engine oil, and superplasticizer)
was used throughout the experiment. Results show that OPC and
OPC/RHA RC beams containing used engine oil and superplasticizer
exhibit higher capacity, 18-26% than their corresponding control
mix.