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Showing 1-5 of 11 Abstracts search results

Document: 

SP243-08

Date: 

April 1, 2007

Author(s):

R.K. Panchalan and V. Ramakrishnan

Publication:

Symposium Papers

Volume:

243

Abstract:

This paper presents the results of an experimental investigation to determine the validity of 0.45-power chart in obtaining the optimized aggregate gradation for improving the strength characteristics of high-performance concrete (HPC). Historically, the 0.45 power chart has been used to develop uniform gradations for asphalt mixture designs; however it has now been widely used to develop uniform gradations for portland cement concrete mixture designs. Some reports have circulated in the industry that plotting the sieve opening raised to the 0.45 power may not be universally applicable for all aggregates. In this paper the validity of 0.45 power chart has been evaluated using quartzite aggregates. Aggregates of different sizes and gradations were blended to fit exactly the gradations of curves raised to 0.35, 0.40, 0.45, 0.50 and 0.55. Five mixtures, which incorporated the aggregate gradations of the five power curves, were made and tested for compressive strength and flexural strength. A control mixture was also made whose aggregate gradations did not match the straight-line gradations of the 0.45 power curve. This was achieved by using a single size aggregate and sand. The water-cement ratio and the cement content were kept constant for all the six mixtures. The results showed that the mixture incorporating the 0.45 power chart gradations gave the highest strength when compared to other power charts and the control concrete. Thus the 0.45 power curve can be adopted with confidence to obtain the densest packing of aggregates and it may be universally applicable for all aggregates.

DOI:

10.14359/18746


Document: 

SP243-10

Date: 

April 1, 2007

Author(s):

L. Coppola, P. Marcassoli, and S. Lorenzi

Publication:

Symposium Papers

Volume:

243

Abstract:

This paper deals with variability in the performances of seven different superplasticizers chosen among those of most common use belonging to the naphthalene (NSF) and polycarboxylate-based (PCE) families. In particular, compatibility of two naphthalene-based and five polycarboxylate-based admixtures with six different cements available on the Italian market was evaluated by measuring water reduction to manufacture mortars with the same workability at the end of mixing. Two different lots of the same cement (same plant) were used: lot 1 and 2 produced, respectively, on September 2005 and March 2006. Flow retention up to sixty minutes and tendency to entrap air in the mortars were measured. Results confirmed that the average water reduction and flow retention properties are better for PCE compared to NSF superplasticizers. However, experimental data confirm as performances of PCE admixtures are more strongly dependent on the cement type than those of NSF polymers. No differences were detected in terms of the air entrapped between the two superplasticizer families, except for the ACR5 superplasticizer.

DOI:

10.14359/18748


Document: 

SP243-04

Date: 

April 1, 2007

Author(s):

V. Ramakrishnan, R. Zellers, and A.K. Patnaik

Publication:

Symposium Papers

Volume:

243

Abstract:

This paper presents the evaluation of a new high tenacity monofilament polypropylene fiber for reduction of plastic shrinkage cracks in concrete. The crack reduction potential of the fiber was studied using cement-rich concrete and the performance of the fiber was compared with that of three other presently available fibers (Fiber B, Fiber C, and Fiber D). Performance of these fibers was evaluated by comparing the area of plastic shrinkage cracks developed in control slabs (with no fibers) with the crack area of fiber reinforced concrete slabs. For example, the reduction of crack area due to the addition of the new high tenacity monofilament fiber was 91 percent for a dosage of 0.593 kg/m3 [1.0 lb/yd3], 86 percent for 0.297 kg/m3 [0.5 lbs/yd3] and 57 percent for 0.196 kg/m3 [0.33 lbs/yd3]. The results indicate that the new fiber with fiber length of about 18 mm [¾ inch], and a fiber dosage of 0.593 kg/m3 [1.0 lb/yd3] was most effective in reducing the plastic shrinkage cracks in concrete. For the same fiber quantity, three other fibers were less effective in reducing cracks.

DOI:

10.14359/18742


Document: 

SP243-03

Date: 

April 1, 2007

Author(s):

M. Hubertova and R. Hela

Publication:

Symposium Papers

Volume:

243

Abstract:

The paper is concerned with the development of lightweight self-consolidating concrete, especially with the comparison of the effect of metakaolin and that of silica fume on the properties of this concrete. The use of metakaolin for improving the durability and for achieving better physico-mechanical properties of concrete is relatively new approach in concrete technology. The experimental works which are described in this paper used for the manufacture of lightweight self-consolidating concrete of different fractions of the expanded clay lightweight aggregate Liapor with different fractions of normalweight aggregate. The metakaolin used was of Czech production.

DOI:

10.14359/18741


Document: 

SP243-06

Date: 

April 1, 2007

Author(s):

B. Persson

Publication:

Symposium Papers

Volume:

243

Abstract:

This article outlines an experimental and numerical study on the optimization of mixture proportions of concrete. For this purpose about 500 mixture proportions were studied in the laboratory and compared with about 500 mixture proportions from industry. Normal, high-performance and self-compacting concrete were included in the investigation. Additives such as fly ash, limestone filler, silica fume and slag and different kinds of cement were included in the program. The w/c varied between 0.15 and 1, with 28-day cylinder strength ranging from 20 to 120 MPa. The results show with high significance that ideal particle distribution curves exist for each cement and concrete type taking into account also the related water demand and the correlation between w/c and strength. The study resulted in a highly efficient commercially available computer program.

DOI:

10.14359/18744


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