• Journal of the Korean Recycled Construction Resources Institute
• /
• v.6 no.3
• /
• pp.102-109
• /
• 2011

In this study, in order to develop ultra rapid hardening mortar(URHM) for tunnel repairs using bottom ash of low recycle ratio and Admixture as Eco concept, watertightness and durability properties of URHM on temperature condition of construction field were performed. Test result, seepage quantity and water absorption coefficient regarding watertightness of URHM were as in the following : series II > series I. Seepage quantity for the standard condition were smaller than low temperatures. all specimens were satisfied below 20g as standards of seepage quantity on KS F 4042. Because of the decrease of unit cement content by to replacement of blast furnace slag, the neutrlization resistance for durability properties was reduced. The result of alkali resistance and acide resistance, compressive strengths for specimens soaked in calcium hydroxide solution of seriesI were lower than compressive strengths for specimens not soaked. On the other hand, the case of series II show that the deterioration of compressive strengths for specimens was not almost showed. Compressive strengths of specimens soaked were similar with specimens not soaked except series II-C in $5^{\circ}C$. Therefore, specimens using both blast furnace slag and bottom ash were good in alkali resistance and acide resistance.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.10 no.2
• /
• pp.47-53
• /
• 2010

Very-early strength latex-modified concrete (VES-LMC) was developed with a focus on workability, strength development and long-term durability that would allow for opening a bridge to traffic only 3 hours after concrete placement, which would be useful when repairing concrete bridge deck overlays. However, even though usage of latex in VES-LMC improves the durability, it has a disadvantage that it produces lots of entrained air. Therefore, specific plan is necessary since it is weak for freezing and thawing in air-void structure. In the present study ultra-fine fly ash (UFFA) was used. Test results are follows ; Air content of VES-LMC UFFA (VES-LMC using UFFA) concrete was decreased since major pozzolan reaction was happened in one day. It was also found that total air content of concrete was decreased with pozzolan reaction since air content in 28 days was the same with one day air content. The addition of calcium hydroxide increased entrained air which is smaller than size of 200 ${\mu}m$. It was effective to improve the air-void structure of VES-LMC since spacing factor can be confirmed as smaller than size of 200 ${\mu}m$ using more than 15% of UFFA.

• International Journal of Highway Engineering
• /
• v.13 no.1
• /
• pp.139-148
• /
• 2011

Asphalt concrete overlay method is used by general maintenance and rehabilitation of construction for aged concrete pavement in Korea. However, in case of the AC overlay method to extend service life of the existing concrete pavements, various distresses of reflection crack, pothole and rutting are the typical problems of the asphalt overlay on existing concrete pavement since it has different physical characteristics between asphalt overlay and existing concrete pavement. To achieve this, application of concrete overlay method is required instead of AC overlay method. Concrete overlay method has advantages that can reduce maintenance cycle and costs since it has excellent bearing value for heavy vehicles and no rutting. However, technical problems of detour road construction, traffic control and other disadvantages happened by long curing time. Thus, in this study and experimental research were launched to evaluate the workability, durability and resistance against environmental loading of Very Rapid Hardening Acrylic Polymer Modified Concrete(VRH-APMC) for application of bonded concrete overlay method. Test results showed that the compressive and bond strength were exceed 21MPa and 1.4MPa of target strength after four hours for rapid traffic opening properties. And tests of resistance against environmental loading results showed that VRH-APMC secured excellent durability. Thus, it was known that VRH-APMC was suitable material for large scale bonded concrete overlay method, and it was possible to use maintenance and rehabilitation method which needs enough workability and rapid traffic opening.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.6 no.1
• /
• pp.128-135
• /
• 2011

In this study, in order to develop ultra rapid hardening mortar(URHM) for tunnel repairs using bottom ash of low recycle ratio and Admixture as Eco concept, fundamental properties of URHM on temperature condition of construction field were performed. Test result, URHM of three types for fluidity and setting time were as in the following : B > C > A. Those for low temperatures were later than the standard condition. Compressive, bending and bond strength were similar with three types as follow. In compressive strength, initial strength of the low were smaller than the standard but the low in the long-term were similar with the standard. On the contrary to this, bending strength were similar in initial strength but the low in the long-term were smaller than the standard. The low in bond strength was average 35% less than the standard. Length changes was as in the following : A > C > B. the low is two times much as the standard but the case using blast furnace slag particles noticeably reduced length changes. Water absorption coefficient and water vapor resistance were as in the following : C > A > B. In case of URHM added bottom ash, water absorption coefficient and water vapor resistance were increased because bottom ash is porous material.

• Journal of the Korean Geosynthetics Society
• /
• v.20 no.4
• /
• pp.133-140
• /
• 2021

There are few attempts to estimate the strength and stiffness of controlled low strength material (CLSM) using existing field-testing methods. The objective of this study is to evaluate the resilient modulus of CLSM by using the Light Weight Deflectometer (LWD) and investigate the relationships between the resilient modulus from LWD and the unconfined compressive strength (UCS) and secant modulus of elasticity from unconfined compressive test. Five CLSMs with different mix designs are used to evaluate the flowability and the stiffening of the CLSM in the flow and Vicat needle tests, respectively. To evaluate the early strength and stiffness characteristics, unconfined compressive tests are performed using the CLSM specimens cured for 1 and 7 days. LWD tests are carried out to estimate the resilient modulus of the CLSM specimens. The experimental results show that for the curing time of 1 day, the UCS and secant modulus of elasticity generally increase with the fast setting mortar content (FC). The CLSM specimen with the highest FC shows the significant increase in the UCS and secant modulus of elasticity along the curing time. Overall, the resilient modulus for the curing time of 1 day increases with the FC, while that for the curing time of 7days decreases with an increase in the FC. From the results, the linear relationships between the resilient modulus and UCS and secant modulus of elasticity are established.

• 한국도로학회:학술대회논문집
• /
• 2009.11a
• /
• pp.501-504
• /
• 2009

• Journal of Industrial Technology
• /
• v.21 no.B
• /
• pp.249-256
• /
• 2001

The purpose of this study was to remove the excessive air foaming which was produced in mixing the RSLMC(latex-modified concrete with rapid-setting cement) by choosing the best antifoam agent type. A series of RSLMM(latex-modified mortar with rapid-setting cement) experiments were carried out as a basic experiments for RSLMC with the main experimental variables such as antifiamer types(A, B, C, D), antifoamer contents(0, 1, 2, 3%), and latex contents(10, 15%). Air content test and compressive strength tests were carried out to measure the improved properties of RSLMM. SEM analysis, also, was carried to observe the formation of latex film. The results of RSLMM showed that the decrease of 50% air content was obtained by admixturing an antifoam agent by 1%. This made the strength enhanced and the workability be within the purposed. The best properties of compressive strengths was obtained at latex content of 15% and D antifoam agent of 1%. compressive strength increased about 32.6%. The analysis of SEM results no difference in a formation of later film.

• Journal of the Korea Institute of Building Construction
• /
• v.7 no.4
• /
• pp.109-116
• /
• 2007

Building structures are generally large in size and have a long life, and the construction of such structures requires the investment of a huge amount of money and social infrastructure. Furthermore, building structures are closely related to people's life. Recently, however, the rapid development of society has been worsening air pollution, which is in turn accelerating the degradation of building structures. Thus, the safety of building structure is emerging as a critical issue. To cope with this problem, the government enacted "The Special Act on Safety Control for Infrastructure" but we need engineers' higher concern over the maintenance and reinforcement of existing structures. Recently researches are being made actively on repair mortar using ultra rapid hardening cement for recovering the performance of structures. The present study conducted an experiment on the basic physical properties of ultra rapid hardening mortar for repairing and reinforcing building structures using magnesia cement and mono-ammonium phosphate. In the experiment, we changed the water-cement ratio and carried out replacement at different ratio of MAP/MgO(%). We used retarder to have working life, and made comparative analysis through evaluating working life and fluidity and measuring strength by age.

• Magazine of the Korea Concrete Institute
• /
• v.2 no.4
• /
• pp.83-90
• /
• 1990

Ultra Rapid Hardening Cement (LJRHC) makes immediate response, cracks and finally collapses in the 5 % acid solution. Such physical and chemical reaction is assumed to occur beCaUSE) it contains calcium aluminate( 11 Cao . 7AI,O, . CaF,) and the hydrate. This experimental study aims to improve URHC by making up for its weakness, which appears when its pro¬perties are compared with other cements properties, in the Polymer Cement Mortar(PCM) The result are : PCM using URHC proved to be inferior to PCM using other cements in the resistance to the acid in that the former cracked and collapsed after 10 days, and 22 days, in P/C=O%, and 5% respectively. And in P/C=15% and 20 % the PCM using URHC proved to be more resistant to the acid.

• Journal of Industrial Technology
• /
• v.27 no.A
• /
• pp.103-110
• /
• 2007

Concrete is a material that will crack during its service life by its very nature. For bridge decks this is especially significant as these cracks allow accelerated ingress of chlorides and the subsequent corrosion of the reinforcing steel and deck deterioration. Very-early strength latex-modified concrete (below ; VES-LMC) was developed in order to realize early-opening-to-traffic bridge deck concrete. Although there has been little research to document the degree of cracking in VES-LMC overlay, there has been a general perception among highway agencies that overlay cracking of VES-LMC, particularly early-age cracking, is a one of problems which should be solved. The purpose of this study was to analyze the cause of map, transverse and longitudinal cracking in VES-LMC and to provide a control methods for minimizing the occurrence of cracks. The proposed prevention against map and transverse cracking was verified by field applications. VES cement was modified, the unit cement contents was reduced into $360kg/m^3$ from $390kg/m^3$, the maximum size of coarse aggregate was increase into 19mm from 13mm, wire mesh and steel fibers were incorporated in concrete mixture.