Mark G. Richardson

Fundamentals of Durable Reinforced Concrete

1. Framework for Durability by Specification 2. Probabilistic Approach to Durability Design 3. Permeability and Transport Processes 4. Corrosion of Reinforcement in Concrete 5. Carbonation 6. Chloride Ingress 7. Alkali-Silica Reaction 8. Freeze/Thaw Effects 9. Chemical Attack - Sulfates 10. Chemical Attack - Acid and Seawater Attack 11. Cracking in Reinforced Concrete Structures 12. Abrasion, Erosion and Cavitation 13. Weathering and Efflorescence

Yield and chemical composition of five common grassland species in response to nitrogen fertiliser application and phenological growth stage

Abstract The interaction of grassland management factors such as plant species, rate of nitrogen (N) fertiliser application and stage of maturity at harvest, will determine the optimal balance of herbage yield, nutritive quality and ensilability for ruminant nutrition and/or industrial applications. This study investigated the effects of N fertiliser input and harvest date on the yield and chemical composition of five common grass species, and made comparisons with red clover. Perennial ryegrass (PRG), Italian ryegrass (IRG), tall fescue, cocksfoot, timothy and red clover were grown under two inorganic N fertiliser inputs (0 kg N ha−1 and 125 kg N ha−1; except red clover) and harvested at five dates (fortnightly from 12 May to 7 July) in the primary growth. Regression analysis of these data allowed comparison of the yield and chemical composition of each grass species at common growth stages, without the confounding effects of variation in maturity between grass species at common harvest dates. Of the grass species investigated, timothy was most productive in terms of dry matter (DM) yield and thus has the potential to provide a cheaper feed per unit DM. However, the most digestible grass species was PRG, with timothy being the lowest, and this could impact on both animal and bioenergy production potential. The most suitable grass species for ensiling was IRG (particularly when grown without fertiliser N) due to its higher water soluble carbohydrate (WSC) concentration and lower buffering capacity (BC) compared to all other grass species. In comparison to the grasses receiving inorganic N fertiliser, red clover had a numerically lower DM yield, but a higher mean DM digestibility and crude protein concentration. The lower WSC concentration and higher BC of the red clover may result in a greater preservation challenge during ensiling.

Reactivity assessment of aggregates : Role of chert crystallinity

No cases of damaging alkali-silica reaction (ASR) have been identified to date in the Republic of Ireland, even though high-alkali-content cements were prevalent for a period and the gravels used contain significant quantities of chert. This article reports on expansion tests that were conducted on Irish aggregates; tests included petrographic examination and mortar bar and concrete prism expansion testing. The authors discuss the systematic assessment scheme for determining the alkali reactivity of aggregates that has been developed for international use. Chert-bearing Irish aggregates performed poorly in expansion tests, despite an exemplary service record. The authors examined chert crystallinity through domain size and quartz crystallinity index. The authors conclude that the poor performance of Irish concretes in the standard international test methods was due to the existence of a critical alkali threshold above that experienced in concrete practice, but below that used in expansion test methods.

Modelling Chloride Ingress in Concrete: A Comparative Study of Laboratory and Field Experience

This paper compares chloride resistance values from lab tests and field trials, derived solely by diffusion-based modeling. Concrete prisms were exposed to sodium chloride solutions in lab tests for 12 months. The trials included both continuous immersion and cyclical wetting and drying cycles. Chloride values were determined at 3, 6, and 12 months. Material variables included portland cement, fly ash, crushed limestone aggregate, natural sand, and natural gravels. Diffusion coefficients were derived through best-fit curves based on Cranks error function solution of Ficks 2nd law of diffusion. It was found that the lab test diffusion coefficients diminished significantly with increases in test duration and stabilized between 6 and 12 months, by which time they yielded values of a similar order of magnitude to those from the structures in service. The coefficients for gravel aggregate concrete specimens were more variable than those for crushed rock aggregate concretes and could exceed the in-service values by a factor of at least two. The beneficial influence of fly ash was reflected in the results.

Assessment of ultrasonic signals to determine the early age properties of concretes incorporating secondary cementitious materials

Summary Secondary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) are used in increasing quantities in concrete practice internationally. While these materials offer benefits such as reduced CO 2 and a more dense microstructure, they also have drawbacks in terms of slower initial gain of strength. There are significant financial implications associated with this, as it can lead to delays in the construction process. Key to overcoming this challenge is the development of a methodology to assess the early-age stiffness development in concretes manufactured using GGBS. This paper presents the results of a study into the application of ultrasonic sensors to assess the early age concrete stiffness. A novel wavelet-based approach is used to overcome the difficulties associated with wave reflections and classical wave theory is used to determine the concrete small-strain stiffness based on P and S wave velocities. It was found that the results are largely in agreement with those obtained using standard strength testing, suggesting potential practical applications of this method.