1887

oa Civil Engineer in South Africa - Surface joint sealants for low head water retaining structures

Volume 24, Issue 5
  • ISSN : 0009-7845

 

Abstract

The effective sealing of joints in concrete structures subjected to low heads of water, such as canals and small off-channel balancing storage reservoirs, has developed into a matter of gathering importance. This is so on account of steeply rising costs of supplying water to consumers. Pumping from storage to storage and conveying water through tunnel systems and long interlinking canals, with the more elaborate and expensive control works they have come to entail, has underlined the increasing need to ensure that seepage losses through open or inadequately sealed canal joints be minimized.


While the engineer has at his disposal a few standard specifications for joint sealants such as those based on polysulphides (whether pure or coal-tar extended), silicone rubbers and oleo-resinous mastics, nothing seems to have been done in South Africa until very recently to investigate further the merits and demerits of a family of low-cost elastomeric joint sealants which could in general be described as 'polymer coal tars', being one-pack heat-curing rubberized coal-tars.
This paper reports on some further evaluation of the practical performance of this sealant material which has very recently been developing in local manufacture and, as hinted at by its description, can have a local raw material content in excess of 95 per cent. It is a hot-pour; sealant and as such is confined in range of practical applications to joints inclined at angles no steeper than about 65o to the horizontal. Hand-screeded concrete lining of water retaining structures seldom exceeds 3 m in depth.
For the Directorate of Water Affairs of the Department of Environment Affairs, the interest, in studying the sealants' performance and practical and economic potential, fell mainly on canals. It was decided to examine, in the Directorate's laboratory, the resistance to extrusion or rupture through typical concrete lining joints under hydraulic pressure. Heads of water of up to 6 m were applied.
The information obtained in this way could serve as a useful adjunct to the physical test results obtained from the SABS laboratories when it comes toadjudicating tenders for the supply of these sealants.

Die doeltreffende verseëling van voeë in lae-druk waterhoudende strukture soos kanale en leidamme het in onlangse tye 'n saak van toenemende belang geword. Die hoofrede hiervoor is die skerpstygende koste van die lewering van water aan die verbruiker. Die pomp daarvan om dit in hoërliggende voorraad te kry en die vervoer daarvan deur tonnelstelsels en lang afstand kanale, met gepaardgaande en duur beheerwerke, onderstreep die noodsaaklikheid om te verseker dat wegsyferingsverliese deur oop of onbehoorlik verseëlde kanaalvoeë tot die minimum beperk word.


Hoewel die ingenieur 'n paar standaard spesifikasies vir voegseelmiddels tot sy beskikking het, soos die van polisulfied (beide suiwer en koolteer bevattende tipes), silikoonrubber en olie-hars kalfaatsels, kom dit voor dat niks tot onlangs gedoen is nie om die gebruike en prestasies van voegseëlmiddels wat as polimeerkooltere beskryf kan word, in Suid-Afrika verder te ondersoek.
Hierdie verhandeling doen verslag oor verdere ondersoekwerk na die evaluering van hierdie materiaal se funksionele doeltreffendheid. Dit word tans in plaaslike vervaardiging verder ontwikkel, en soos die beskrywing dit te kenne wil gee, kan die plaaslike rou materiale inhoud daarvan hoër wees as 95 persent. Dit word warm gegiet en as sulks word die praktiese gebruik daarvan beperk, soverre dit voeë betref, tot hellings van nagenoeg 65o of platter.
Handbeklede betonvoerings in kanale en klein balanseerdamme, soos wat in die Direktoraat van Waterwese van die Departement van Omgewingsake op grootskaal aangebou word, het selde 'n totale diepte van meer as 3 m en daar was gevolglik besluit om die hidrouliese druktoetsprogram, om die materiaal se weerstand teen uitpers of skeur te ondersoek, op 'n werksdruk van 3 m te baseer. Hidrouliese toetsdrukke tot op 6 m is aangewend.
Die inligting wat hierdeur ingewin word kan as 'n nuttige aanvulling dien tot die fisiese toetsuitslae wat voorsien word deur die SABS en tot hulp wees met die beoordeling van tenders vir die verskaffing van hierdie tipe voegseëlmiddel.

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/content/civeng1/24/5/EJC24880
1982-05-01
2016-12-10

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