The Charles Bridge in Prague

  

The Prague castle is the oldest standing bridge over the river Vltava in Prague and it is the second oldest preserved bridge in the Czech Republic. The Charles Bridge substituted the previous Judith bridge which was broken down during the spring thaw in 1342. The Charles Bridge construction was started, under the auspices of the Charles IV king of Bohemia and Holy Roman Emperor, by the foundation stone laying down in 1357. The construction of the bridge was finished in 1402.

The Charles bridge is 515.76 m long and 9.40 – 9.50 m wide. The height of the pavement is 13 m above the normal water level. It is created by 16 arches. Their span is 16.62 m – 23.38 m. Bridge pillars were not founded in the rock because it was too deep. Therefore the bridge was founded in the foundation pit on running stones which were supported by oak piles. The bridge is made of blocks from different types of sandstones which make the framework; most of the pillars are bricked. There are also three towers on the bridge.
Building investigation in 1966-1967 revealed that the bridge was endangered especially by small cracks which allowed ingress of rainwater with soluble salts used for the winter pavement maintenance.
It was decided that the bridge opening had to be blocked off by the framework of anchors.

Probably since 2001 specialists and also the public authorities and Prague citizens have been discussing about subsequent repairs of the bridge. The previous capital repair had some problems: the waterproofing treatment under the pavement did not perform very well and did not prevent the rainwater ingress into the construction.
In 2004-2005 the last repair intervention schedule was set down. Finishing building investigation and gathering complete documentation had to be done in 2005 and 2006. In 2006 the first two pillars (the eighth and ninth from the Little Quarter side) were anchored to concrete sarcophaguses.
The bridge masonry repair is considered to be the most difficult phase of the whole repair. Every stone block was investigated by experts who decided whether it was to preserve, clean or substitute.
The upper construction repair started in August 2007 and took approximately 3 years.

Two different aspects were solved in the first phase of the bridge pillars repair. The first one was the appropriate formula of the mortar to be used under water level (some pillars under water level), which would have met the requirements for the permanent contact with water and would feature higher abrasion resistance and sufficient strength.

A wall made of steel casing was built up around the pillars in order to increase their protection and resistance and MAPEGROUT T60 sulphateresistant shrinkage-compensated fibre-reinforced thixotropic mortar was used for the repairs. The second aspect was to find the substitution of the original historical mortar for walling and grouting of the sandstone masonry above water level (only with random flooding during spring thaw).

MAPE-ANTIQUE LC was used in this case, salt resistant, hydraulic binder based on lime and eco-pozzolan, cement-free, mixed with local aggregates in various grain sizes to reproduce the original mortar. MAPE_ANTIQUE I, super-fluid, salt-resistant, fillerized hydraulic binder, based on lime and eco-pozzolan was used for consolidating masonry by injection of some sections in the bridge pillars.