Kyong-Ku Yun

A Case Study of Concrete Pavement Deterioration by Alkali-Silica Reaction in Korea

The concrete pavement of the Seohae Highway in Korea has suffered from serious distress, only four to seven years after construction. Deterioration due to Alkali-Silica Reaction (ASR) has seldom been reported per se in Korea, because the aggregate used for the cement concrete has been considered safe against alkali-silica reaction so far. The purpose of this study is to examine the deterioration caused by an alkali-silica reaction of concrete pavement in Korea. The investigation methods included visual inspection and Automatic Road Analyzer (ARAN) analysis of surface cracks, coring for internal cracks, stereo microscopic analysis, scanning electronic microscope (SEM) analysis, and electron dispersive X-ray spectrometer (EDX) analysis. The results are presented as follows: the crack pattern of the concrete pavement in Korea was longitudinal cracking, map cracking or D-cracking. Local areas of damage were noticed four to five years after construction. The cracks started from edges or joints and spread out to slabs. The most intensive cracking was observed at the intersection of the transverse and longitudinal joints. Where cracking was the most intense, pieces of concrete and aggregate had spalled away from top surface and joint interface area. The progress of deterioration was very fast. The reaction product of alkali-silica gel was clearly identified by its generally colorless, white, or very pale yellow hue seen through a stereo optical microscopy. The typical locations of the reaction product were at the interface between aggregate and cement paste in a shape of a rim, within aggregate particles in the cracks, and in the large void in the cement paste. Most of the white products were found at interface or internal aggregates. SEM and EDX analysis confirmed that the white gel was a typical reaction product of ASR. The ASR gel in Korea mainly consisted of Silicate (Si) and Potassium (K) from the cement. The crack in the concrete pavement was caused by ASR. It seems that Korea is no longer safe from alkali-silica reaction.

Evaluation of Air Void System and Permeability of Latex-Modified Concrete by Image Analysis Method

Addition of latex to concrete is known to increase its durability and permeability. The purpose of this study is to analyze air void systems in latex-modified concretes using a reasonable and objective method of image analysis with such experimental variables as water-cement (w/c) ratios, latex contents (0%, 15%) and cement types (ordinary portland cement (OPC), high-early strength (HES) cement and very-early strength (VES) cement). The results are analyzed by spacing factor, air volume (content) after hardening, air void distribution and structure. Additionally, air void systems and permeability of latex-modified concrete (LMC) are compared by a correlation analysis. The results are as follows. The LMC of the same w/c ratio showed better air entraining (AE) effect than OPC with AE water reducer. The VES-LMC showed that the quantity of entrained air below increased more than four times. For the case of HES-LMC, microscopic entrained air between the range of 50 to increased greater than 7 times even in the absence of anti-foamer. Although spacing factor was measured rather low, the permeability of latex-modified concrete was good. It is construed that air void system does not have a considerable effect on the property of latex-modified concrete, but latex film (membrane) has a definite influence on the durability of LMC.

DURABILITY OF VERY-EARLY-STRENGTH LATEX-MODIFIED CONCRETE AGAINST FREEZE-THAW AND CHEMICALS

This study focused on the durability of very-early-strength latex-modified concrete against freeze-thaw and chemical exposure by using water absorption, freeze-thaw resistance, deicer salt scaling, and chemical resistance tests. The experimental variables were latex content (latex solids and cement as percentages) and water-cement ratio (w/c). This study examined five levels of latex content (0%, 5%, 10%, 15%, and 20%) at a constant slump and three w/cs (0.36, 0.38, and 0.40) at a constant latex content of 15%. The results were as follows: the water absorption at 15% latex content was less than 50% at 0% latex content and supported the theory of a continuous polymer film that hinders the penetration of water. Within the range of this study, both the latex-modified and nonmodified concrete exhibited good freeze-thaw performance, although the latex-modified exhibited superior properties. In both the weight loss and visual evaluations, the deicer salt scaling test indicated improved performance as the latex content increased. In the chemical resistance tests, the weight loss of latex-modified concrete decreased as the latex content increased for both sulfuric and hydrogen chloride acid exposures. However, in the calcium chloride solution test, the weight change varied from a slight gain with no latex to a slight loss at 20%.

Hygral Behavior of Superabsorbent Polymers with Various Particle Sizes and Cross-Linking Densities

This study focuses on investigating the effects of particle size and cross-linking density on the hygral behavior of superabsorbent polymers (SAPs), which are increasingly used as an internal curing material for high-performance concrete. Four SAPs with different mean particle diameters and cross-linking densities were tested under controlled wetting and drying conditions to measure free absorption and desorption kinetics. Absorption capacities of SAPs under actual mixing conditions were additionally measured and verified by means of mortar flow and semi-adiabatic hydration heat measurements. In addition, the effects of SAP type and dosage (i.e., 0.2, 0.4, and 0.6% by mass of cement) on the mechanical properties of hardened mortar were assessed. The results indicated that: (1) the absorption capacity increased with decreased cross-linking density and increased particle size under both load-free and mixing conditions; and (2) the greater the cross-linking density and the lower the particle size, the shorter the desorption time. It was also confirmed that while the early-age mechanical properties were more related with the gel strength of swollen SAP, the later-age mechanical properties were more affected by the water retention capacity and spatial distribution of SAP in the matrix.

Expansion Behavior of Aggregate of Korea due to Alkali-Silica Reaction by ASTM C 1260 Method

This study was performed to proof expansion effect of the mortar bar due to Alkali-silica Reaction (ASR) by ASTM C 1260 test. Recently, the failure case of cement concrete pavement by ASR was reported in Korea. Cement concrete structures are caused crack by ASR. The service life of cracked cement concrete structures by ASR will be shorted. In this study,crushed the slate rock producted Chungcheongnamdo Boryeong was caused 0.3% expansion at 14days due to ASR by ASTM C 1260 test. The particular spectrum showed that the ASR gel wasanalyzed contents included Si, Na, K, and Ca by EDX (electron dispersive X-ray spectrometer). It was verified that the crushed aggregate was caused expansion by ASR in Korea.

Thermal and Autogenous Shrinkages of Very Early Strength Latex-Modified Concrete

A study evaluated the factors influencing thermal and autogenous shrinkages of very early strength latex-modified concrete (VES-LMC) with respect to latex content (latex solids-cement ratio, by weight); water-cement ratio; retarder content (retarder solids-cement ratio, by weight); and antifoamer content (antifoamer-latex solids ratio, by weight). Examined were three levels of latex content (0%, 5%, 15%) at a constant slump, three levels of water-cement ratio (0.34, 0.38, 0.42) at a constant latex content of 15%, three levels of retarder content (0.0%, 0.3%, 0.6%), and three levels of antifoamer content (0.0%, 0.5% and 1.0%) at a constant latex content and water-cement ratio. Results were that total shrinkage was governed by thermal deformation at very early age because of the high heat of hydration of VES cement. After 5 h, total shrinkage was governed by the autogenous shrinkage process. The absolute magnitude of thermal expansion was 130 micro strains while the autogenous shrinkage was 120 micro strains. The autogenous shrinkage increased as latex content increased. VES-LM concrete with a high latex content and low water-cement ratio caused autogenous shrinkage. The total and autogenous shrinkages of VES-LMC were not affected or only slightly affected by the water-cement ratio or the antifoamer content. Excessive retarder induced expansion at very early age, which increased the absolute shrinkage. Thus, attention should be paid whenever retarder is added in response to weather conditions. Furthermore, immediate and proper wet curing is necessary when adding more retarder because of greater susceptibility to plastic shrinkage.

Early-Age Shrinkage and Durability of Shotcrete with Expansive Agent

In this dissertation, the shrinkage and durability of shotcrete were examined. Analysis and comparison of shrinkage against the strength of shotcrete was investigated after performing actual shotcrete shooting for each mix of different percentage of expansive agent. The research on restrained shrinkage with different percentages of expansive agent used (3%, 7%, 11% and 15%) shows that the maximum shrinkage in all samples occurred in between 13-15 hrs after shotcrete shooting. And it is noticed that increasing the percentage of expansive agent can lower the shrinkage. And hence, the 15% of expansive agent not only lowered the shrinkage But it also lowered the strength.

Evaluation of Alkali-Silica Reactivity for Aggregates in Korea according to Test Methods

The purpose of this study was to evaluate the alkali-silica reactivity for aggregates in Korea according to test methods: accelerated mortar bar test (AMBT) by ASTM C 1260; chemical test by KS F 2545 (ASTM C 289). The results are as follows: The AMBT (ASTM C 1260) results showed that two (2) igneous rocks (two mica granite and felsite), three (3) sedimentary rocks (arkose, red sandstone and shale), two (2) metamorphic rock (slate and vitric tuff), one (1) mineral (quartz) showed more expansion than 0.1% at 14 days. But, some sedimentary rocks and metamorphic rocks expanded more than 0.1% at 28 days even though they were less than 0.1% at 14 days. Therefore, it is necessary to extend the experimental dates more than 14 days to evaluate the possibility of alkali-aggregate reactivity. The chemical test (KS F 2545) results showed that five (5) igneous rocks (andesite, diabase, granite porphyry, muscovite granite and diorite) were indicative of potentially deleterious expansion, while two (2) igneous rocks (diorite porphyry and quartz porphyry) were possible indicative of expansion, and three (3) igneous rocks (biotite granite, two mica granite and felsite) were indicative of innocuous reactivity. The above results showed that the results from chemical method (KS F 2545) and AMBT (ASTM C 1260) had little relationship.

Analysis of Air Voids System Using Image Analysis Technique in Hardened Concrete

Air voids in hardened concrete have an important influence on concrete durability such as freeze-thaw resistance, surface scaling resistance, and water permeability, and they have been characterized by spacing factor Linear traverse and point count methods in ASTM standard have been used in estimating an air void system in hardened concrete. However, these methods require lots of time and efforts, further they are not repeatable. Image analysis method could be utilized In estimating an air void systems in hardened concrete with a developments of microscope, digital camera and computer program. The purpose of this study was to develope image analysis method and provide a guideline by comparing the results from ASTM method and image analysis method. The concerns were at air void content and diameter distribution, air voids system as well as spacing factors. The experimental variables included air content by air entrained agent (0, 0.01, ) and depth of specimen (top, middle, bottom). The result showed that it was possible to calculate spacing factor using image analysis technique, as well as air content, air diameter distribution, and air structure. This study also contributed in developing an reasonable and repeatable image analysis method.

Comparison of Static and Dynamic Strains of Asphalt Concrete Pavement from FWD Tests

A series of Falling Wieght Deflectometer (FWD) tests is conducted on an instrumented asphalt concrete section on a test tract in the PACCAR Technical Center in Mount Vernon, Washington. Horizontal strain measurements are taken from strain gauges in pavement cores in Fall, Winter, late Spring and early Summer conditions. This paper presents results from the field tests and compares them with static and dynamic theoretical predictions using CEVRON and SAPSI computer programs respectively. CHEVRON is a well known pavement analysis computer program which uses static, linear, layered-elastic theory, and SAPSI is a computer program for the dynamic analysis of asphalt concrete pavements by the linear damped-elastic layer theory and the finite element method. The results indicate that static analysis using statically back-calculated layer moduli seems to be sufficient in analyzing FWD field tests, despite the fact that static back-calculation using FWD (dynamic) deflections will lead to “stiffened” elastic properties. Ninety percent of measured strains in October 1991 and in June 1992 were within ±10 percent error of their calculated values, versus 70 percent within ±20 percent error in February 1993.