Limestone aggregate

At the end of forties several cases of hmestone aggregate concretes destmction have been documented in North America. Initially this was attributed to the poor aggregate resistance to fieezing and thawing. However, already in 1957 Swenson [140] proved that the limestone aggregate swelling was the result of reaction with alkalis from cement. 

All reactive carbonate rocks in the world have similar composition and texture. These are the dolomitic hmestones contaminated with clays, showing very fine texture. They are composed of dolomite crystals scattered in a matrix built of clay minerals and calcite pelite. Most of them reveal good physical properties, primarily high strength, low absorbabihty, high density and hence they can be used in the production of high quality aggregate. 

There are various hypotheses explaining this aggregate expansion mechanism. The most wide spread refer to the swelling of clay minerals and of osmotic pressure formation [141,142]. All these hypotheses agree that this phenomenon relates to the reaction of soluble alkalis from cement with the aggregate leading to the decomposition of dolomite  

However, Swenson [140] had shown that the decomposition of dolomite alone does not cause expansion. 

These experiments, though the further studies and observations are required, can have a serious practical importance, because the expansion of carbonate aggregates is more difificirlt to control. The pozzolanic additives moderate this effect only in the case when the Na O. in cement is lower than 0.4 [98]. 

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Concreteyiggregate. A versatile appHcafion for coarse limestone aggregate is in Pordand cement concrete, either job-mixed or ready-mixed for a wide variety of concrete appHcafions, such as footings, poured foundations, paving, curbs, stmctural products, etc. Limestone sand also provides a satisfactory fine aggregate, but usually it is more cosdy than conventional sand from local pits. 

Concrete Products. Limestone aggregate is used competitively with other aggregate in the manufacture of molded, reinforced, and prestressed concrete products in the form of block, brick, pipe, panels, beams, etc. 

A concrete consists of 60% by volume of limestone aggregate plus 40% by volume of cement paste. Estimate the Young s modulus of the concrete, given that E for limestone is 63 GPa and E for cement paste is 25 GPa. 

Adopting a lightweight or limestone aggregate, which is less susceptible to spalling than a siliceous aggregate such as flint. 

James, J. G. and Broad, B. A. Transport and Road Research Laboratory, TRRL Supplementary Report 635 (1980) Conveyance of coarse particle solids by hydraulic pipeline Trials with limestone aggregates in 102, 156 and 207 mm diameter pipes. 

Figure 4. Marshall stability vs. compaction tem-perature—limestone aggregate...

Figure 6. Voids content vs. compaction temperature—limestone aggregate...

Figure 9. (a) (above) Stress fatigue curve—limestone aggregate, (b) (below) Stress fatigue curve—volcanic aggregate. 

L) = type IVb limestone aggregate, (V) = type IVb volcanic aggregate. b Prepared in Barber-Greene Mixall. c Prepared in Essick mortar mixer. 

Characterization tests reported here were performed on combinations of materials needed to evaluate the predicted performance of typical pavements made from conventional asphaltic concrete with limestone aggregate, sulfur-asphalt concrete with limestone aggregate, sulfur-asphalt concrete with beach sand aggregate, and recycled asphaltic concrete pavement with sulfur added during the recycling process. The data... 

Test methods for limestone aggregates and natural calcium carbonates are specified in the relevant parts of BS 812 [6.3] and BS 6463 [6.5]. The former is being replaced by CEN Standards that are in preparation (see section 6.5). BS 6463, Part 102 (also in preparation) refers to CEN test methods, where appropriate (see below). 

In the production of limestone aggregate, the selection of appropriate crushers (see section 5.2) helps to ensure an acceptable particle shape. Well designed screens help to ensure that the aggregate is of the correct size and that it has a low content of fines and clay, all of which have a marked effect on the water demand for a given workability. The strength and durability of the hardened concrete is generally related to the water demand. 

Crushed, dense limestone aggregates are generally suitable for such applications. 

In order to improve the resistance of sewers the use of concrete with limestone aggregate is recommended [71]. The oxidation of strlphides with chlorine and whitewash, to raise the pH value over 10, is another remedial method [222]. The systematic removal of slime and mud to accelerate the flow, but with maintaining its laminar character, is recommended too [222]. Surface sewer walls treatment, particularly with gaseous SiF can be also used [222]. 

Fig. 9.5 Compressive strength of calcium aluminate cement concretes (according to [21]) 1 limestone aggregate, cement content 350 kg/m, w/c = 0.5, 2 crushed limestone aggregate, w/c=0.6, 3 siliceous aggregate with ground limestone, 4 siliceous boulders, w/c = 0.54, 5 siliceous aggregate,...

A sufficient quantity of the selected emulsifier should be included in the emulsion so that a sufficient number of free molecules of the emulsifier exist. The pH of the aqueous solution of the emulsifier should fluctuate depending, mainly, on the chemical composition of the bitumen and the type of aggregates. Regarding the effect of the aggregate type on the adhesiveness of the emulsion/bitumen, it should be stated that cationic emulsions adhere very well to all types of aggregates for the production of bituminous mixtures. In contrast, anionic ones adhere better only to limestone aggregates. 

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