Tag Archive for Tag: concrete

Tag: concrete Concrete Masonry Units

Materials and Manufacturing of Concrete Masonry Units Concrete masonry units are formed from zero-slump concrete, sometimes using lightweight aggregate. The concrete mixture is usually vibrated under pressure in multiple-block molds. After stripping the molds, the units are usually cured under atmospheric conditions in a chamber that is maintained at warm and humid conditions by the presence of the curing units. Atmospheric steam

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Tag: concrete Polymer impregnated concrete

A polymer impregnated concrete is produced via a process whereby an existing hardened concrete (structure or factory component) is dried at around 150ëC and then impregnated with a low viscosity monomer, usually methyl methacrylate, which is subsequently cured in situ. Impregnation is often achieved by soaking at atmospheric pressure although the process may be facilitated by evacuation and/or higher pressures.

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Tag: concrete Polymer-modified cement, mortar and concrete Nature of systems

Widespread international use is made of these materials, e.g. as grouts and mortar patches for finish and repair work and concretes for bridge deck overlays. Basically, unreactive polymer latex is added to the water of a fairly conventional cementitious mix, which is then cured. The cement begins to hydrate, whilst the polymer particles from the latex coalesce to give a

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Tag: concrete Concrete and aggregate Specification issues in Standard EN 206-1

The prescriptive approach to durability in EN 206-1 maintains the durability grade principle of Deacon and Dewar (1982) that underpins the advice in concrete design standards such as those published in the UK since the 1980s. This approach is based on the principle that a clear relationship exists between durability expectation and minimum concrete grade, minimum binder content and maximum

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Tag: concrete Testing of fresh concrete

The most commonly employed tests on fresh air entrained concrete measure the total air content. The pressure method, described in ASTM C231, is widely used and is based on Boyle’s Law. It is assumed that solid constituents in fresh concrete and water are incompressible so that volume change under pressure is due to the contraction of air voids. Volume change

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Tag: concrete Degradation of concrete in cold weather conditions Introduction

Concrete and cement composites are forgiving materials and the expectation of a long service life at an extreme ambient temperature is not unreasonable. Extreme temperatures in hot and cold climates do not in themselves present a threat because dry concrete has an acceptably low coefficient of thermal expansion and moderate movements can be taken into consideration in design. A durability

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Tag: concrete Limiting the alkali content of the concrete

Stanton’s (1940) formative work on ASR indicated that expansive reaction is unlikely to occur when the alkali content of the cement is below 0.60% Na2Oe. This value has become the accepted maximum limit for cement to be used with reactive aggregates in the United States, and appears in ASTM C 150 Standard Specification for Portland cement as an optional limit

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Tag: concrete Test methods for identifying aggregate reactivity

The first step in assessing the potential of an aggregate for AAR expansion and cracking is the performance of a petrographic analysis by a trained petrographer, the methodology being as recommended by a RILEM technical committee (Sims and Nixon, 2003). However, a petrographic analysis may not identify certain reactive materials (some may not be readily identified by optical microscopy), and

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Tag: concrete Manifestations of aggregate-related damage in field concrete

The extent of damage caused by frost-susceptible aggregates in field concretes is dependent on the exposure conditions of the concrete, the proximity of such aggregates to the exposed surface, and the quality (especially permeability) of the mortar layer above and surrounding the aggregates. Although the distress can be throughout the concrete in extreme cases, many instances of aggregate- related problems

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Tag: concrete General requirements of aggregates for use in concrete

Although most issues related to frost resistance of concrete are associated with damage emanating from the paste (e.g., due to internal disruption or surface scaling), there are cases where the aggregates, themselves, either exhibit distress or cause distress of the surrounding paste. This section discusses the basic mechanisms responsible for this aggregate-related distress and describes the manifestations of such distress in

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