- Open Access
Low Carbon Concrete Prepared with Scattering-Filling Coarse Aggregate Process
© The Author(s) 2014
- Received: 6 December 2013
- Accepted: 7 May 2014
- Published: 11 June 2014
The volume fraction of the coarse aggregate in the conventional plastic concrete is controlled relatively low to ensure a required workability. In this paper, a new type of coarse aggregate interlocking concrete with strength ranging from C30 to C80 was prepared with scattering-filling aggregate process. The strength of concrete prepared with this method increases obviously whereas the shrinkage decreases significantly, the cement dosage in the concrete decreased 20 % at the same time. The micro-hardness of the ITZ between the cement paste and scattering-filling aggregate is higher than that of the original aggregate, the ITZ become narrower and tighter also. The interlocking and more even distribution of the coarse aggregate and the water absorption of the addition of extra amount of coarse aggregates contribute to the strength and performance improvement of the concrete prepared with scattering-filling aggregate process.
- coarse aggregates
- scattering-filling aggregate process
- aggregate interlocking concrete
- interfacial transition zone
The physics technique properties of cements.
Normal consistency %
Initial setting time Min
Final setting time Min
3d strength (flexural/compressive) Mpa
28d strength (flexural/compressive) Mpa
The chemical compositions of raw materials.
The fly ash supplied by Xiangfan Thermoelectric Plant was used in this investigation. The 0.045 mm screen residue of the fly ash was 4.7 %. The chemical compositions of those materials are presented in Table 2.
Four kinds of coarse aggregates were used in this investigation, they were 10–30 mm crushed limestone (LS-1), 10–30 mm gravel (GS-1), 20–40 mm crushed limestone (LS-2) and 20–40 mm diabase crushed stone (DS-1). Two kinds of fine aggregates were used in this investigation, they were yellow sand (YS) with a fineness modulus of 2.74 and dark sand (DS) with a fineness modulus of 2.19. A polynaphthalene sulphonate superplasticizer with a trade name as FDN was used in this investigation.
The aggregate interlocking concrete test cubes were prepared by a simulating scattering-filling aggregate process in the laboratory. First a conventional concrete mixture was prepared with the general process. One layer of this mixture was scattered in the bottom of the mould, following by a layer of coarse aggregates, a further layer of mixture and another layer of coarse aggregates. Generally with three layers of aggregates scattered in each 150 × 150 × 150 mm3 mould, then vibrated the moulds for 40–75 s till the concretes were consolidated.
The mixture proportions of the concretes and the sorts of the adding aggregates.
Fly ash kg/m3
Silica Fume kg/m3
Coarse aggregate kg/m3
Sand ratio %
Adding aggregate sort
2.3 Items of Investigation
The compressive strength of the concrete: At the age of 7, 28 days, concrete specimens were tested for compressive strength respectively, three 150 × 150 × 150 mm3 were tested for each date point.
Shrinkage specimens of the three prisms with a size of 100 × 100 × 515 mm3 were tested for each date point after being cured in a chamber with 60 % relative humidity. Three specimens were tested for each date point.
The micro-hardness was measured by a HXS-1000 Vickers Micro-hardness Meter Produced in Shanghai Shangguang microscopy Lt.D, which is an average of 3 points for a data points (Beste and Jacobson 2003). In the experiment, the testing point distributed across the aggregate and cement paste interfacial transition zone to measure the hardness distribution of ITZ of different concrete sample.
3.1 The Effect of the Adding Aggregate Volume on the Concrete Strength
It can be found that the strengths of all those concretes with different mix proportions increase obviously with the 20 % (the volume ratio of scattering concrete in the finished concrete) adding aggregate ratio only different in the extent. The increasing ratio can be as high as 25 %. It is easy to find that concretes with 50–100 MPa have been prepared with only 362–440 kg/m3 of cement or binder when 20 % coarse aggregate is scattered to substitute the original concrete mixtures through some simple calculation, this can be never achieved with the conventional concrete placing process. The scattering-filling coarse aggregate can prepare concrete with very high coarse aggregate, although the “pre-placed aggregate” concrete process (Neville 1981) can prepare concrete with as low cement dosage as this process, but it can only prepare low or middle strength concrete. The scattering-filling aggregate method can produce consolidated concrete with less cement but higher strength and performances at the same time, the decrease on cement dosage not only give the concrete good cost competitive but also good environmental harmonization. The optimal volume percentage of the scattering aggregate in the concrete depends on the void ratio of coarse aggregate in the original concrete and the flowability of the concrete, the looser the aggregated packs and the more flowable, the more the scattering aggregate can be added, around 5–12 % of aggregate can be scattered in the pavement concrete. The scattering-filling aggregate process can be potentially apply in nearly all kind of conventional plastic and flowing concrete, is especially suitable to be used in pumped concrete for its high mortar content.
3.2 The Shrinkage of the Coarse Aggregate Interlocking Concrete
Figure 3 indicates that with the increase of the replacement volume fraction of the scattering-filling aggregate, the shrinkage of the concrete decreases significantly. With increasing of the volume fraction of the extra coarse aggregate is added to the concrete, the shrinkage of the concrete decreases markedly. The aggregate scattering-filling process is a very effective approach to reduce the shrinkage of the high strength concrete, which is highly desired by engineers (Mindess et al. 2003).
3.3 The Micro-Hardness Distribution of the Aggregate Paste ITZ
3.4 The Mechanism of the Coarse Aggregate Interlocking Concrete
There are many kinds of process to produce concrete with high coarse aggregate volume fraction, e.g. pre-placing aggregate concrete, Roller-compacted concrete, and some concrete with low cement content (Neville 1981; Ping and Beaudoin 1992; Nadeau 2003). Unfortunately, those processes typically can only prepare low or middle strength concrete (Neville 1981), the result of Fig. 2 indicated that concrete with a strength degrade ranging from C30 to C80 MPa can be prepared with this scattering-filling coarse aggregate process although this kind of aggregate interlocking concrete has very low cement dosage. The mechanism of the concrete process can be explained with following three aspects.
First of all, the coarse aggregate volume fraction increases dramatically in this type of concrete when more than 20 % of coarse aggregate is scattered in the mixture, the coarse aggregates can interlock with each other, the friction forces among the aggregate contribute to the strength enhance in a certain extent. The second, the coarse aggregate distributes more evenly in this kind of concrete than the concrete prepared with conventional process. With the vibration, the segregation of the coarse aggregate toward the bottom of the form and the of the cement paste toward the top may result in the conventional concrete (Mindess et al. 2003), the surface of the concrete will be very weak, but when scatting-filling process is applied, the coarse aggregate will fill evenly at the top of the form. The third, the addition of extra amount of air dry coarse aggregates acts as somewhat water reducer, not only reduces the W/C of the paste close to the aggregate and make the paste stronger so the ITZ of the concrete is enhanced. With the volume fraction of the aggregate increasing, as a composite material, the concrete will become stronger and stiffer.
C30–C80 concrete with higher strength is prepared but lower cement dosage is prepared with scattering-filling aggregate method.
The dry shrinkage of the aggregate interlocking concrete decrease with the increase of volume ratio of the extra adding aggregate.
The surfaces and the pores of the adding aggregates absorb water from cement paste around them, so much tighter and narrower ITZ is formed in the scattering-filling aggregate concrete.
The interlocking, more even distribution of the coarse aggregates and the water absorption of the extra adding aggregate contributed to the strength and performances improvement of this new type of concrete.
The author acknowledges the funding support of Hubei Highway Bureau, the funding support of Guangdong Transportation Ministry 2011-03-057 and 2012-03-006.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.
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