Kazuyuki Torii

Effects of fly ash and silica fume on the resistance of mortar to sulfuric acid and sulfate attack

Changes in physical and chemical properties in the mortars with different replacements by fly ash and silica fume when immersed in 2 % H[sub 2]SO[sub 4], 10 % Na[sub 2]SO[sub 4] and 10% MgSO[sub 4] solutions for 3 years were investigated. The long-term exposure test data showed that the replacement of portland cement by fly ash and silica fume effectively improved the resistance of the mortar to the sulfuric acid and sulfate solution attack. However, the replacement percentage by fly ash and silica fume necessary to prevent the sulfuric acid and sulfate solution attack varied significantly depending on the type of sulfuric acid and sulfate solutions.

Sulfate resistance of high fly ash content concrete

Changes in length, compressive strength, dynamic modulus of elasticity and pulse velocity of high fly ash content concrete with replacement levels of up to 50 % when completely immersed in the 10% Na{sub 2}SO{sub 4} solution were periodically measured for 2 years. It was found from the measurements of mechanical properties that the 50% replacement by fly ash was very effective in the improvement of the sulfate resistance of concrete. During 2 years of exposure to the 10% Na{sub 2}SO{sub 4} solution, high fly ash content concrete with the binder content of 400 kg/m{sup 3} and with replacement level of 50% was steadily gaining the compressive strength, and no detectable deterioration was observed. Chemical analysis data also showed that the excellence of high fly ash content concrete in the sulfate resistance was attributed primarily to the prevention of ingress of sulfate ions into concrete, resulting in little formation of gypsum and/or ettringite in concrete.

Characterization of ecocement pastes and mortars produced from incinerated ashes

In this study, the microstructure and the hydration characteristics of the pastes using ecocement, which is a new type of hydraulic cement, produced with incinerator ashes, limestone and clay was investigated. In addition, the beneficial effect of granulated blast-furnace slag on this new type of cement was also investigated in comparison to ordinary portland cement (OPC). Several tests including AC impedance spectroscopy, mercury intrusion porosimetry, X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC) were used for the study. The results of the various tests were discussed in a complementary manner; in particular, the results of the AC impedance were discussed in conjunction with that of the mercury intrusion porosimetry in order to gain insight into the interpretation of impedance spectrum plots in a physical manner.

Strength development of high strength concretes with and without silica fume under the influence of high hydration temperatures

Abstract High performance concretes of high compressive strength are finding increasing applications in many fields of construction such as core walls and columns in tall buildings, long-span bridges and marine structures. In thick cross-sections, the high binder contents of some high strength concretes can result in the development of high in-situ temperatures. The combined influence of limited moist curing and high hydration temperatures may significantly influence the progress of hydration. This can affect the long-term development of in-situ strength and other engineering properties. Knowledge of in-situ strength development under these conditions is needed to ensure safe utilisation of this new generation of construction materials. This paper presents results of an investigation on the strength development of high strength concretes with and without silica fume subjected to high in-situ temperature conditions. A temperature match conditioning (TMC) system was developed and used to simulate the semi-adiabatic temperature development within medium sized high strength concrete columns. The results of this investigation show that in-situ temperatures of up to 70 °C significantly increased the 7-day strength of a high strength silica fume concrete. Although no strength regression was observed up to 1 year, the silica fume concrete subjected to high early temperatures showed significantly lower strengths when compared to concrete cured at standard temperature. For the silica fume concrete subjected to high early temperatures, non-evaporable water contents suggest little additional hydration beyond 3 days.

Pore structure and chloride ion permeability of mortars containing silica fume

Abstract The addition of silica fume in concrete causes a remarkable increase in strength and a drastic reduction in chloride ion permeability. These effects may be due primarily to microstructural changes both in the cement paste phase and in the interfacial zone around aggregates. The standard method of test for rapid determination of the chloride permeability of concrete, AASHTO T 277–831, has increasingly been used to evaluate the permeability of concrete. However, for the concrete containing silica fume, the results of the AASHTO T 277–831 test, which is expressed in terms of electrical charge passed, do not necessarily reflect the real diffusion index of chloride ion through the concrete. There seems to be factors other than the pore structure which govern the results of the AASHTO T 277–831 test in the concrete containing silica fume. In this study, the effects of silica fume to reduce the chloride ion permeability of the mortar were investigated based on the results of pore size distribution measurements, X-ray diffraction analysis, SEM observations and pore solution extraction. The application of the AASHTO T 277–831 test to the evaluation of the chloride ion permeability of the concrete containing silica fume was discussed.

Chloride ingress and steel corrosion in cement mortars incorporating low-quality fly ashes

In this study, the microstructure and hydration characteristics of ecocement and normal Portland cement mortars blended with low-quality fly ashes were investigated. In addition, the corrosive behaviours of steel bars embedded in the mortars were studied. Several tests including scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC) were used for the characterization of the mortars. Electrochemical measurement such as linear polarization resistance and AC impedance spectroscopy were also used to monitor the corrosive behaviours of the embedded steel bars in the mortars. The chloride ingress into the mortars was also studied. The results of the various tests are discussed.

Chloride Permeability Of Concrete Containing A Flyash And A Blastfurnace Slag

The effects of curing conditions on the chloride permeability of concrete with various replacements of Portland cement by a flyash and a blastfurnace slag was investigated. In order to relate the porosity and pore size distribution of concretes to their chloride permeability, mercury intrusion porosimetry measurements were also conducted. The results showed that exposure of concretes to a relatively low humidity at early ages increased their chloride permeability. It was also found that the chloride permeability of concrete increased proportionally with increasing volume of pores larger than 0.1 μm in diameter.

COMPATIBILITY BETWEEN ECOCEMENT PRODUCED FROM INCINERATOR ASH AND REACTIVE AGGREGATES IN ASR EXPANSION OF MORTARS

Abstract Recently, in Japan, two new-type hydraulic cements, high early strength type ecocement (HEC) and normal type ecocement (NEC), have been developed using incinerator ashes up to 50% of the raw materials. In this study, the compatibility of these ecocements with various types of reactive aggregates with respect to alkali–silica reaction (ASR) was studied. Ordinary Portland cement (OPC) and blast furnace slag cement (BFSC) were also used for a comparative study. Two types of the accelerated mortar bar expansion test, the JIS A1146 and the Danish methods, were used to clarify the expansion behavior of mortars made with the above cements. The influence of a combination of the chemical and mineralogical compositions of cement and the reactive components of aggregate on both the amount of ASR gel and the expansion rate of the mortar was also investigated. From the results, it was found that the expansion behaviors of mortars due to ASR varied significantly depending on a combination of both the mineralogical composition of cement and the reactive component of aggregate.

Load Bearing Capacity of PC Girders with and Without Fly Ash Affected by ASR Deteriorations

Alkali-silica reaction (ASR) is one of the prominent explanations of concrete degradation. Many reactive aggregates are widely distributed to various places in Japan. Especially, in Hokuriku region along the Sea of Japan, there is a wide spread of andesite which accelerates the ASR-induced expansion of concrete. The aim of this study is to investigate how the structural behavior and the load bearing capacity of prestressed concrete (PC) girders, which were affected by varying degrees of ASR-induced damages, change with and without of fly ash. In order to achieve the above purpose, this study conducted full-scale destructive tests of prestressed concrete girders. Specifically, two PC girders, which were constructed and placed outside the laboratory, had been exposed to weather conditions. The first girder was affected by alkali-silica reaction while the second one was kept at an inactive state with ASR acceleration due to the addition of fly ash. As an outcome, it was noticed that the elastic and ultimate states of the full-scale PC girders were well illustrated by the experimental data. In addition, since difference behaviors were well observed, fly ash played significant effects on the performance of the PC girders subjected to ASR deteriorations.

Current Status of Degraded Road Bridge Slab Located in Mountainous Area

In the mountainous area of the Hokuriku region, bridges are suffering early deterioration caused by salt damage, alkali-silica reaction (ASR) and frost damage. Under such a regional situation, the load carrying capacity evaluation of these bridges has become an urgent issue. In this study, a statistical method–survival analysis–was carried out by using inspection data for bridges in the Hokuriku region, and the relationship between degradation tendency of bridges and regional characteristics causing salt damage, ASR and frost damage has been studied. In addition, the degradation causes of the reinforced concrete deck of a road bridge which deteriorated early in the mountainous area of the Hokuriku region were investigated. Cylindrical core extraction was carried out to analyze the degradation causes. Polarizing microscopic observation of specimens collected from RC slabs confirmed that cracks developed from the andesite particles and cracks were confirmed to be filled with ASR gels. Therefore, ASR was a cause of the deterioration. Moreover, the degradation in the mechanical properties of concrete due to ASR was also studied and reported. The results show that the reduction in compressive strength and static elastic modulus of both dry and leakage-water parts affected the load bearing capacity of the structure.