• Computers and Concrete
• /
• v.20 no.2
• /
• pp.145-154
• /
• 2017

In geological engineering, grouting with Portland cement is a common technique for ground improvement, during which micro-fine cement is applied as a slurry, such that it intrudes into soil voids and decreases soil porosity. To determine the utility and behavior of cements with different Blaine values (index of cement particle fineness) for stabilization of fine sand, non-destructive and destructive tests were employed, such as laser-ray determination of grain size distribution, and sedimentation, permeability, and compressive strength tests. The results of the experimental study demonstrated a suitable mix design for the upper and lower regions of the cement-grading curve that are important for grouting and stabilization. Increasing the fineness of the cement decreased the permeability and increased the compressive strength of grouted sand samples considerably after two weeks. Moreover, relative to finer (higher Blaine value) or coarser (lower Blaine value) cements, cement with a Blaine value of $5,100cm^2/g$ was optimal for void reduction in a grouted soil mass. Overall, study results indicate that cement with an optimum Blaine value can be used to satisfy the designed geotechnical criteria.

• Korean Journal of Metals and Materials
• /
• v.46 no.7
• /
• pp.437-442
• /
• 2008

The synthesis and hydration of Calcium Sulfo Aluminate[$3CaO{\cdot}3Al_2O_3{\cdot}CaSO_4(C_4A_3{\overline{S}})$, CSA cement utilizing secondary steelmaking refining slags is studied for recycling the discarded steel plant wastes to meet the environmental requrations imposed on the steel industry. Raw materials of secondary refining slag, lime sludge, gypsum and bauxite were prepared to be sintered at $1,250^{\circ}C$. The sintered samples were hydrated for 1, 3 and 7 days to evaluate the mineralogical and physico-mechanical properties. The hydration products evaluated with the aid of SEM and XRD analyses confirmed the formation and the continuing growth of ettringite phase with the further hydration times, which plays a role in developing the early strength and the expansion properties of cements. The physico-mechanical properties of hydrated CSA products employing the recycled steelmaking refining slags determined in terms of compressive strength and linear expansion of hydrated products are found to be superior to those of the Ordinary Portland Cement(OPC) or the other commercial CSA cements.

• International Journal of Concrete Structures and Materials
• /
• v.9 no.2
• /
• pp.241-254
• /
• 2015

A lot of reinforced concrete (RC) structures in Syria went out of service after a few years of construction. This was mainly due to reinforcement corrosion or chemical attack on concrete. The use of blended cements is growing rapidly in the construction industry due to economical, ecological and technical benefits. Syria is relatively rich in scoria. In the study, mortar/concrete specimens were produced with seven types of cement: one plain Portland cement (control) and six blended cements with replacement levels ranging from 10 to 35 %. Rapid chloride penetration test was carried in accordance with ASTM C 1202 after two curing times of 28 and 90 days. The effect on the resistance of concrete against damage caused by corrosion of the embedded steel has been investigated using an accelerated corrosion test by impressing a constant anodic potential. The variation of current with time and time to failure of RC specimens were determined at 28 and 90 days curing. In addition, effects of aggressive acidic environments on mortars were investigated through 100 days of exposure to 5 % $H_2SO_4$, 10 % HCl, 5 % $HNO_3$ and 10 % $CH_3COOH$ solutions. Evaluation of sulfate resistance of mortars was also performed by immersing in 5 % $Na_2SO_4$ solution for 52 weeks. Test results reveal that the resistance to chloride penetration of concrete improves substantially with the increase of replacement level, and the concretes containing scoria based-blended cements, especially CEM II/B-P, exhibited corrosion initiation periods several times longer than the control mix. Further, an increase in scoria addition improves the acid resistance of mortar, especially in the early days of exposure, whereas after a long period of continuous exposure all specimens show the same behavior against the acid attack. According to results of sulfate resistance, CEM II/B-P can be used instead of SRPC in sulfate-bearing environments.

• Computers and Concrete
• /
• v.24 no.5
• /
• pp.453-458
• /
• 2019

Today, concrete remains the most important, durable, and reliable material that has been used in the construction sector, making it the most commonly used material after water. However, cement continues to exert many negative effects on the environment, including the production of carbon dioxide (CO2), which pollutes the atmosphere. Cement production is costly, and it also consumes energy and natural non- renewable resources, which are critical for sustainability. These factors represent the motivation for researchers to examine the various alternatives that can reduce the effects on the environment, natural resources, and energy consumption and enhance the mechanical properties of concrete. Geopolymer is one alternative that has been investigated; this can be produced using aluminosilicate materials such as low calcium (class F) FA, Ultra-Fine GGBS, and high calcium FA (class C, which are available worldwide as industrial, agricultural byproducts.). It has a high percentage of silica and alumina, which react with alkaline solution (activators). Aluminosilicate gel, which forms as a result of this reaction, is an effective binding material for the concrete. This paper presents an up-to-date review regarding the important engineering properties of geopolymer formed by FA and slag binders; the findings demonstrate that this type of geopolymer could be an adequate alternative to ordinary Portland cement (OPC). Due to the significant positive mechanical properties of slag-FA geopolymer cements and their positive effects on the environment, it represents a material that could potentially be used in the construction industry.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.345-348
• /
• 2008

A Cement account for the most amount than other materials in the material composition of ultra-high-performance concrete. If we especially consider the effect of high temperature curing on the cement hydration and the problems of autogenous shrinkage, heat of hydration we need selection of proper cement type by grasping influence of cement in the properties of UHPC. Therefore, in this paper we examined properties of fluidity, compressive strength and elastic modulus of UHPC due to domestic portland cement types. In results, we could get a result that the low heat cement increase fluidity, compressive strength in UHPC compare with high early strength cement and ordinary portland cement. we are systematically going to examination on the influence of UHPC by domestic portland cement types.

• Applied Chemistry for Engineering
• /
• v.3 no.1
• /
• pp.148-155
• /
• 1992

For the enhancement of the concrete durability, we developed high - durable portland cement (ACTPC) by physical treatment of ordinary portland cement with asphalt and carbon black. In this research, the hydration reaction characteristics of ACTPC were studied by using SEM, X-Ray, Conduction Micro Calolimeter etc. When the ACTPC is mixed with water, it is believed the asphalt films on cement particles suppress the early stage of hydration reactions of cements, because the films hinder the contact with water and the elusion of soluble ions from particles. But the carbon blacks on the cement particles accelerated the hydration reactions of cement after a while, because the micro particles can be used as seed crystals in $CaO-SiO_2-H_2O$ gel formation.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.786-789
• /
• 2004

Corrosion of reinforced concrete structures in marine environment is one of the most important mechanism of deterioration. However, conventional rehabilitation techniques in tidal zone, which consist of removing delaminated areas of concrete, cleaning affected steel and patching with portland cements mortar, have proven to be ineffective for marine structures. Also, repairs are often repeated every several years. The purpose of this report is to announce appropriate repair method of highway bridge damaged by chloride attack in marine environment (application of cathodic protection) using FRP and antiwashout underwater mortar.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.261-264
• /
• 2003

Cold weather can lead to many problems in mixing, placing, setting time, and curing of concrete that can have harmful effects on its properties and service life. Korean Concrete Institute (KCI) defines cold weather as a period when the average daily air temperature is less $4^{\circ}C$ and recommends to cast concrete with special care such as shielding, heating and so on. The use of high early strength cements may improve the rate of hardening characteristics of concrete in cold weather by making it possible to achieve faster setting time and evolving more hydration heat than ordinary Portland cement. Higher early strength can be achieved using Type III cement especially during the first 7 days. The strength increase property of Type III cement at low temperature was studied. As a conclusion the heat or heat insulation curing period can be reduced to 50~75%. So, it can be used for cold weather concreting to reduce construction cost and extend the construction season.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.11a
• /
• pp.74-77
• /
• 2003

This paper investigated the apparent chloride diffusivity of various concretes. Ten mixtures of concrete were initially prepared and tested to estimate diffusion property. The penetration depth and concentration of chloride ion were examined at the same water-binder ration. The binders were composed of normal portland cement, fly ash, ground granulated blast-furnace slag, and silica fume. From the results, it was concluded that using the mineral admixtures had a filling effect on the pore structure of cements matrix due to those pozzoanic reaction with the hydrates of cement, which increases the tortuosity of pore and makes large pore finer. And diffusivity of chloride is following: NPC100 > F10N90 > F30N70 > F20N80 > F20S05 > G30N70 > F10S05 > G30S05 > G30F15 > G50N50.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1997.10a
• /
• pp.539-545
• /
• 1997

Since the length of massive wall-structure is generally longer and larger than its thickness and a lift height of concrete of placement, cracks induced by hydration heat are governed by outer structural restriction rather than inner one. However, the degree of restriction control is expected to be affected by the sizes of wall thickness, length and a lift height. Thus, this analytical study aims at the development of relationship among those to minimize thermal cracks. In addition, the effect of types of cement on the thermal heats and stresses is evaluated for anti-sulphate and 2blended Portland cements concrete. It was found from analytical study that a lift height of concrete placement is the most important factor controlling thermal cracks, and the increase of lift heights is not always detrimental to structural safety.