International Concrete Abstracts Portal

In most existing standards and guidelines, durability of reinforced concrete structures is covered by prescriptive requirements. For corrosion initiated by carbonation, this may include requirements on w/cm, type and content of cement, compressive strength, concrete cover etc. Future requirements will probably be performance based, defined according to a probabilistic approach. However, today we don’t have the appropriate information on the correlation between carbonation rate and factors like w/cm, type and content of cement and environmental situation, especially air humidity and CO2 concentration. Therefore, requirements in standards are still prescriptive. However, the pre- scriptive specifications within codes and standards may be based on testing of existing structures and using a probabilistic approach when analysing the results. A probabilistic approach to the process of defining prescriptive requirements for concrete exposed to carbonation, is presented. The approach is based on the philosophy given in the European standard EN 1990 (1) "Basic of Structural Design," which means that the "failure" reliability Z is calculated as the difference between a resistance against "failure" R (e.g., concrete cover) and an environmental load or action F (e.g., time dependent carbonation depth). Both resistance and load are expressed in a probabilistic way. The new European standard EN 206-1 (2) is used as example, but the presented principle may be used in other situations.

One of the major concerns during application of cementitious grouts inside his- toric masonry is the possible presence of gypsum, which may lead to the creation of ettringite and the subsequent damage of the masonry. The design conccpt ofthe presented hydraulic grouts is based on the reduction ofthe portland cement content to the 30%-wt of the total hinder mass, in favour of appropriately proportioned mixtures of hydrated lime and natural and artificial (silica fume) pozzolans. The behaviour of the system lime-pozzolan-ponland cement in the presence of gypsum is investigated. A series of mortar specimens are made, in which a part of the sand is replaced by gypsum. The various grouts are used as hinders. The evolution of the length change and the modulus of elasticity are followed for 730 days. A very big expansion is recorded in the Iime-natural pozzolan-portland cement mortars, which may be considered as non-sulfate resistant. On the contrary, the substitution of a part of the natural pozzolan (10%-wt of the pozzolan) by an equal in weight amount of silica fume leads to a drastic reduction of the recorded expansions.

This paper presents the results of an investigation undenaken to develop addi- tional data on the chemical and mechanical properties on porous concrete. When immersed in seawater for a period of 360 days, the compressive strength of porous concrete decreased by about 15 to 20% compared with standard curing, due to the leaching of free lime. Abrasion resistance of porous concrete in water showed a slightly lower value compared with that of normal concrete. The dynamic modulus of elasticity shows a steep rise during early periods up to 7 days. This tendency became more noticeable when the binder-voids ratio was decreased. The resistance of porous concrete to freezing and thawing is considered to be low, because porous concrete has continuous voids into which water can permeate during freezing and thawing. Increasing the binder per unit volume of porous concrete increases its durability.

Chloride induced reinforcement corrosion represents an enormous problem world-wide. The exposure conditions for concrete structures in the Persian Gulf area constitute one of the most aggressive climatic environments in the world. In this region, interaction between concrete and environment controls material performance and has resulted in premature deterioration and low durability of concrete structures and is of major concern. This paper reports experience from in-situ investigations on the effects of differ- ent dosages of silica fume and also a surface coating system applied to concrete decks in Persian Gulf area. The specimens were kept in various placement conditions: fully submerged zone, tidal zone, atmospheric zone, underground zone and laboratory conditions. The focus is placed on the abilitv to prevent chloride ingress. Moreover, the test results have been compared to numerical results obtained, using Life-365 model proposed by Thomas and Bentz.

Wick action is defined as the transport of water (together with any dissolved salts) through a concrete element from a face in contact with water to a drying face. This study investigated the depth of chloride penetration in a range of concrete types exposed to salt water with and without wick action. Concretes containing normal portland cement (NPC) only, silica fume and ground granulated blast-furnace slag (GGBS) were tested. Initial moisture content and cementitious type were found to influence water and chloride transport. The relative performance of the various concrete types is discussed together with possible reasons for the observations and implications for in-situ performance.