Archive for Construction

The Power of Pozzolans

 

The use of lime dates back to pre-historic times. Lime is derived from limestone, a sedimentary rock formed mainly of skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different forms of calcium carbonate.

It is generally held that the Greeks began the large scale production of lime-based mortars in Europe and it was from there that the technology spread to Rome.

The Romans early recognized the need for a mortar that could be used under ground and under water – the development of hydraulic mortars is credited to them and the use of Pozzolans was crucial for this.

 

Pozzolana

 

Pozzolans would include volcanic ash or clay brick/tile dust – these would be added to the lime mortar mix to create a faster set and reduce the mortar’s vulnerability to frost and rain.

Vitrivius describe Pozzolans as producing “astonishing results” and he explains the process behind them:

 

The Ten Books on Architecture, Vitrivius

 

Lime Pozzolan binders are obtained by the addition of a Pozzolan (natural or artificial) to the lime while mixing mortar. A natural Pozzolan is a volcanic material, which originally derives from Pozzuoli, an Italian region around Vesuvius. Pozzuoli earth was used in the Roman mortars but other natural Pozzolan are Santorini earth (Greece) and trass (Germany).

Artificial Pozzolans include metakaolin, silica fume, brick dust (preferably low fired brick) and others such as fly ash.

 

Caesarea is the earliest known example to have used underwater Roman concrete technology on such a large scale. Photo by James Cocks www.jamescocks.com.

 

Pozzolans became the backbone of Roman construction and were incorporated in the ‘Roman Concrete’.

Pozzolans of Pozzuoli were used to build ‘La Via Appia’, the Colosseum and the Pantheon of Rome. The fact that the mix could harden under water allowed the Romans to extend their empire along their coastines which gave them a strategic advantage.

Interestingly, lime Pozzolan concrete still has a place in today’s construction technology, not only because of its original characteristics but particularly because it can also offer significant carbon savings and potentially present huge environmental benefits. After all, lime is a remarkably efficient natural absorber of carbon dioxide and it could sequester carbon emissions in a very effective way.

Interesting readings:

 

3 Things You Didn’t Know Architects Do #3

 

The Architect has very considerable powers under the Building Contract although is not a party to it.

The Architect must act upon a fair and proper interpretation of the contract as an independent observer. S/he must act fairly and impartially between the parties.

Contract administration can be quite complex and this (short) post by no means explores all that is involved. We just want to highlight 3 things you (probably) didn’t know architects do when they are appointed for the Construction Stage of your project:

1. Prepare the Building Contract

2. Issue Certificates for Payment to the Contractor

3. Issue Instructions to the Contractor

Under the standard RIAI Building contracts the Architect/Contract Administrator has the power to issue instructions to the contractor.

Instructions may relate to:

  • the modification of the design, quality or quantity of the works or the addition, omission or substituition of any work (“Variations”);
  • the correction of discrepancies between the contract documents;
  • the removal of materials from site;
  • the opening up for inspection of any work covered up;
  • the removal and/or re-execution of of any work not in accordance with the contract;
  • the postponement of work;
  • the dismissal of incompetent or misconducting personnel;
  • the amending and making good of any defects;
  • and any other matters relating to the proper execution of the contract.

The Contractor has the duty to comply and duly execute any work comprised in such Architect’s Instructions.

Click here to see a sample of Architect’s Instructions.

 

 

3 Things You Didn’t Know Architects Do #2

 

From the Employer’s initial brief through to project completion the Architect undertakes a myriad of processes.

Many of the conditions in standard forms of building contract relate to financial matters, and Architects need to have a comprehensive knowledge and understanding of them and be able to apply those conditions properly and in a professional manner.

Contract administration can be quite complex and this (short) post by no means explores all that is involved. We just want to highlight 3 things you (probably) didn’t know architects do when they are appointed for the Construction Stage of your project:

1. Prepare the Building Contract

2. Issue Certificates for Payment to the Contractor

Certification and making decisions are important duties for the Contract Administrator (the Architect). Certification requires the Architect to exercise judgement on various matters arising from the performance of the contract. The Architect has to issue interim certificates stating the amount due to the contractor. This amount shall be the total value of the work duly executed and of materials and goods delivered to site, less an amount to be retained by the Employer. The certificate must be factual and accurate, as the Architect may be personally liable for errors in certification.

The Architect/Contract Administrator typically sends the Certificate to the Contractor. After this the Contractor is entitled to send his invoice together with the Certificate to the Employer. The Employer shall honour the Certificate within 7 working days of the certificate.

3. Issue Instructions to the Contractor

 

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