• Computers and Concrete
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• v.15 no.2
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• pp.167-181
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• 2015

"Mortar or concrete pneumatically projected at high velocity onto a surface" is called Shotcrete. Models that predict shotcrete design parameters (e.g. compressive strength, slump etc) from any mixing proportions of admixtures could save considerable experimentation time consumed during trial and error based procedures. Artificial Neural Network (ANN) has been widely used for similar purposes; however, such models have been rarely applied on shotcrete design. In this study 19 samples of shotcrete test panels with varying quantities of water, steel fibers and silica fume were used to determine their slump, cost and compressive strength at different ages. A number of 3-layer Back propagation Neural Network (BPNN) models of different network architectures were used to train the network using 15 samples, while 4 samples were randomly chosen to validate the model. The predicted compressive strength from linear regression lacked accuracy with $R^2$ value of 0.36. Whereas, outputs from 3-5-3 ANN architecture gave higher correlations of $R^2$ = 0.99, 0.95 and 0.98 for compressive strength, cost and slump parameters of the training data and corresponding $R^2$ values of 0.99, 0.99 and 0.90 for the validation dataset. Sensitivity analysis of output variables using ANN can unfold the nonlinear cause and effect relationship for otherwise obscure ANN model.

• Journal of the Korean Ceramic Society
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• v.37 no.8
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• pp.751-759
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• 2000

Effects of the dosage change, from 0 to 2.0 wt% based on cement weight, of naphthalenic (NSF) and polycarboxylic(NT-2) superplasticizers, on the fluidity of cement paste substituted by 10 wt% II-anhydrite and fly ash respectively as well as II-anhydrite and fly ash itself were investigated. Dispersion properties between particles in suspension were investigated by zeta potential test. Initial fluidity and slump loss in the paste system were observed through mini-slump and apparent viscosity changes with elapsed time. Zeta potential on the particle surface was a tendency to increase according to increasing of NSF dosage. Especially, zeta potential of fly ash has the highest value among all particles equivalent to NSF dosage. In the fluidity of cement paste substituted by inorganic particles, the specimen with substitution of 10 wt% II-anhydrite and fly ash for cement was more effective than cement itself to improve initial fluidity and retain stable fluidity of cement paste. In addition, effect of NT-2 and NSF to improve the fluidity of cement paste, addition of 1.0 wt% NT-2 was more effective than 1.5wt% NSF.

• International Journal of Concrete Structures and Materials
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• v.2 no.1
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• pp.41-48
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• 2008

This study investigates the spalling properties of high strength concrete designed with various types of mineral admixture and diverse content ratios of polypropylene (PP) fiber. Experimental factors considered in series I are four pozzolan types of mineral admixture and series II consists of three shrinkage reducing types of mineral admixture. PP fiber was added 0.05, 0.10 and 0.15vol. % in each mixture of series I and series II, so that totally 27 specimens including control concretes in each series were prepared. Test results showed that the increase of fiber content decreased the slump flow of fresh concrete and increased or decreased the air content depending on the declining ratio of slump flow. For the properties of compressive strength, all specimens were indicated at around 50 MPa, which is high strength range; especially all specimens in series II were 60 MPa. Fire test was conducted in standard heating curve of ISO 834 with ${\phi}100{\times}200\;mm$ size of cylinder moulds for 1 hour. The specimens incorporating silica fume exhibited severe spalling and most specimens without the silica fume could be protected from the spalling occurrence in only 0.05vol % of PP fiber content. This fire test results demonstrated that the spalling occurrence in high strength concrete was not only affected by concrete strength related to the porosity of microstructure but also, even more influenced by micro pore structure induced by the mineral admixtures.

• Advances in concrete construction
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• v.4 no.1
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• pp.49-69
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• 2016

This work investigates the mechanical properties of conventional concrete (CC) and self compacting concrete (SCC) using fine rubber and silpozz were accompanied by a comparative study between conventional rubberized concrete (CRC) and self compacting rubberized concrete (SCRC). Fine rubber (FR) from scrap tires has replaced the fine aggregate (FA) and Silpozz has been used as a replacement of cement at the proportions of 5, 10 and 15%. Silpozz as a partial replacement of cement in addition of superplasticiser (SP) increases the strength of concrete. Fresh concrete properties such as slump test, compaction factor test for CRC, whereas for SCRC slump flow, $T_{500}$, V-funnel, L-box, U-box, J-ring tests were conducted along with the hardened properties tests like compressive, split tensile and flexural strength test at 7, 28 and 90 days of curing. The durability and microstructural behavior for both CRC and SCRC were investigated. FR used in the present study is 4.75 mm passing with fineness modulus 4.74.M30 grade concrete is used with a mix proportion of 1:1.44:2.91 and w/c ratio as 0.43. The results indicate that as FR quantity increases, workability of both CRC and SCRC decreases. The results also show that the replacement of natural fine aggregate (NFA) with FR particles decreases the compressive strength with the increase of flexural strength observed upto 5% replacement of FR. Also replacement of cement with silpozz resulted enhancement of strength in SCRC.

• Computers and Concrete
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• v.31 no.2
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• pp.97-110
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• 2023

This study investigates experimentally the impact of magnetized water (MW) on the fresh and hardened characteristics of concrete. Five types of MW are produced using magnetic fields of 1.4 and 1.6 Tesla for treating water with 100, 150, and 250 cycles. The concrete properties are assessed using the slump test, compressive strength test, scanning electron microscopy (SEM) analysis, energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectrophotometry (FTIR). Furthermore, the chemical-physical characteristics of tap water (TW) and MW are evaluated. The results showed the magnetic field intensity has a significant impact on the magnetization effect; the best magnetizing conditions were found when TW was exposed successively to magnetic fields of 1.6 T and 1.4 T for 150 cycles. In addition, 150 MW cycles can be used to improve the compressive strength and workability of concrete by 40% and 17%, respectively. pH, total dissolved solids, and electrical conductivity improved by 15%, 17%, and 7%, respectively, when using MW. Additionally, MW can be used to enhance cement hydration chemical processes and made concrete's structure denser.

• Advances in concrete construction
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• v.16 no.1
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• pp.59-68
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• 2023

In the pumping process, concrete moves along the pipe and experiences both pressure and shear. This changes the workability and flow characteristics of the concrete. However, the effect of pressure and shear on the change in properties of concrete during the pumping process has not yet been accurately identified. This study analyzed the effects of pressure and shear on the properties of concrete during pumping. For quantitative tests, lab-scale test equipment capable of simulating the pressure and shear applied to concrete during pumping was used. For one coarse aggregate type, two paste types, three mortar types, and five concrete types, the effects of pressure, shear, and shear under pressure conditions were examined by varying the maximum pressure (0 to 200 bar) and the rotational speed of the vane for shear (0 to 180 rpm). Under the maximum pressure condition of 200 bar, the water absorption of coarse aggregate increased by 0.62% and that of fine aggregate also increased. When the concrete was under pressure, significant changes (a reduction in a slump and an increase in viscosity and yield stress) compared with the effect of the elapsed time occurred owing to an increase in the water absorption of the aggregates. When both pressure and shear were applied to concrete, both the slump and viscosity decreased. As the rotational speed of the vane increased, changes in properties became significant. Shearing in the absence of pressure maintained the properties of concrete. However, shearing under pressure conditions caused a reduction in slump and viscosity.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.51-56
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• 1993

This is a part a study on the development of High-Performance Concrete ; about experimental results from several test methods to estimate workability in fresh concrete and influences of concrete mix design that affects properties of super-flowing concrete. Super-flowing concrete can be filled in a formwork without any vibration because of its excellent workability of passing narrow space and filling complicated shaped mold, new test methods should be used to estimate the workability and rhelogy in super-flowing concrete instead of slump test method in conventional concrete.

• International Journal of Concrete Structures and Materials
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• v.8 no.2
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• pp.165-172
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• 2014

Recycled coarse aggregate (RCA) made from waste concrete is not a suitable structural material as it has high absorption of cement mortar, which adheres on the aggregate surface and on the tiny cracks thereon. Therefore, when using RCA made from waste concrete, much water must be added with the concrete, and slump loss occurs when transporting. Hence, its workability is significantly worse than that of other materials. In this study, surface of RCA was coated with water-soluble polycarboxylate (PC) dispersant so that its characteristics improved. Each possibility was evaluated: whether its slump loss can be controlled, by measuring its workability based on the elapsed time; and whether it can be used as a structural material, by measuring its strength. Moreover, the carbonation due to cement mortar adhesion was measured through a carbonation test. As a result, RCA coated with PC dispersant was found to be better than crushed coarse aggregate and RCA when the physical properties of the fresh concrete and the mechanical, durability of the hardened concrete were tested.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.203-208
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• 1994

These tests were conducted to get a device high strength concrete products in factory using admixtures for high strength concrete. The superplasticzer was used to compensate low slump of base concrete keeping its slump up about $6\pm1cm$. To examine the property for strength revelation of concrete using admixtures for high strength concrete, steam and standard curing were compared each other. Test results show that admixtures for high strength concrete is effective in steam curing and compressive strength 500kgf/$\textrm{cm}^2$ is obtained at one day, 650kgf/$\textrm{cm}^2$ at 28days as added to concrete at the ratio of 10-15%, and 740kgf/$\textrm{cm}^2$ at the ratio of 30%. Therefore admixtures for high strength concrete is effective in steam curing and make it possible to get high strength concrete using only steam curing not using autoclave curing.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1059-1064
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• 2001

This study is about accurate steel column position method in the Top down method's delicate part. When the concrete is placing, it is required that complementary measures to the transformation due to concrete pressure, column buckling, the trouble due to bar net inserting and so on. To solve the problem of exist method, the concrete is placed at the bottom of excavated hole in advance. then, the steel column is inserted into the excavated hole. With a new method try, the problem due to placing pressure and others is could be prevented. In this study, the concrete is examined with test-slump, slump flow, and compressive strength to do quantitative analysis of concrete. The factors of the experiment is plasticizer, retarder addition rate, fly ash substitution rate to cement. Considering of the new method try, the retarder added concrete properties-fluidity, viscosity, strength-is investigated as time lapsing.