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Architectural concrete

The modern-day language of architects

Architectural Concrete - The modern-day language of architects

Whether it is at breathtaking heights or through extreme forms and structures – the visions of architects for the realisation of museums, concert halls, stadiums or bridges place the highest possible demands on the construction industry around the world. In many cases, architectural concrete is the modern solution, whether it is for civil engineering, economic or aesthetic reasons.

PERI provides its customers in the construction industry with practical help and support: selection, planning and supply of formlining and formwork systems which are optimally matched to the project requirements. The right formwork solution for every architectural concrete surface, from standard formwork to special designs. The best results arise from the very close cooperation between architects, contractors and PERI engineers.

Architectural concrete - The modern-day language of architects
Praxishandbuch - Sichtbeton

Best Practice for Architectural Concrete

More than 100 pages of valuable expert knowledge – concise, instructive and practice-oriented.

 

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Definition of "Architectural Concrete"


Münstertor

Architectural concrete has become increasingly more important in recent years. Today, visible concrete surfaces are in great demand both as a stylistic means as well as a design form of modern architecture.

The architectural concrete surface is the area of concrete that remains unconcealed after completion that shows the characteristics of the design and manufacture (e.g. form, texture, colour, formlining, joints) and which plays a decisive role in determining the architectural impression of a structural component or structure. A wide range of architectural concrete surfaces can be achieved through the use of special formwork and specific concrete composition among other things.

In order to realise an architectural concrete surface, the following questions have to be clarified:

  • Which quality features should the architectural concrete surface exhibit?
  • Which requirements are to be specified in the tender documents?
  • Which requirements are placed on the formwork in order to form the concrete surface?
  • Which requirements are placed on the concrete formulation, manufacture and placing of the concrete?


For architectural concrete surfaces, the following design possibilities are available:

  • Formwork impressions (formlining)
  • Surface structure of the formlining
  • Fixing of the formlining
  • Pattern of panel and formlining joints
  • Arrangement and design of tie points
  • Special concrete formulations
  • Choice of cement, aggregate granulation and colour, concrete additives and more.
  • Surface coating through covering paint or a translucent colour on the concrete surface
  • Colour additives in the concrete result in integrally-coloured concrete


Subsequent surface treatment through:
 

  • washing
  • cleaving
  • pointing
  • granulating
  • chiselling
  • sandblasting
  • acid washing
  • sanding
  • polishing
  • flame-cleaning
  • rolling
  • smoothing
  • brooming

The architectural concrete team


For a structure / structural component with particular concrete surface requirements, coordinated co-operation of everyone involved in the planning and execution is essential.

The expectations and requirements of the planners and client must correspond to that which can be realized in the actual execution. In addition to the contractual and legal framework, the planner is well advised to co-ordinate his expectations with the specialists in the architectural concrete team.

As a general rule, the contract is not allocated in the planning phase which means that no final decision has been taken regarding who will carry out the work. It is possible that, for example, a consultation agreement can be concluded with a competent specialist company such as a formwork or formlining manufacturer.

A consultancy contract can be signed with an engineering office experienced in the execution of architectural concrete structural components. This engineering office will then assume the role of architectural concrete coordinator in the architectural concrete team – see diagram below. The partners should work together in an architectural concrete team.


Planning


Client

Expresses his wishes for the structure / structural component as well as providing the financial framework.

Architect

Creates the design for the structure / structural component based on these wishes and defines the concrete surface requirements.

Structural Engineer

Calculates the executable, load-bearing construction and creates the implementation plans; with SB 3 and SB 4 concrete, the forming plans should ideally include all information necessary to create the cubic volume in the building shell. These are: construction joints, tie arrangement, formlining joints, mounting parts and recesses of any size (including light switches, sockets, etc.) for walls and slabs.


Execution

 

Contractor

Has the task of constructing the building according to the client's wishes in accordance with the design, construction and the agreed price. He works together, among others, with the following cooperation partners:

Formwork provider

Plans the formwork required according to the project specifications with:

  • Selection of the formwork system as well as the type of formlining
  • Joint pattern and joint configuration unless specified by the planner
  • Tie pattern and tie configuration unless specified by the planner
  • Supplies the formwork in accordance with the agreed delivery conditions.

Concrete supplier

Delivers the concrete which has the required properties for the described structure / structural component.


Monitoring


Concrete engineer

  • Has extensive knowledge of concrete regarding composition, production, processing and testing
  • Ensures and supervises that the materials for the concrete are suitable and that these can be technically implemented, as well as selecting an appropriate type of concrete
  • Ensures and supervises the careful placing of the concrete, together with adequate and suitable protection, until it has sufficiently hardened (curing)

Architectural concrete coordinator

  • Leads the architectural concrete team and coordinates the work carried out by the partners
  • Accompanies and checks all planning and construction stages which includes, among other things, lack of information and missing details in the planning and specifications
  • Determines the most suitable formwork and formlining together with the contractor / formwork provider
  • Inspects the structural component, and that the reinforcement can be concreted

The role of the architectural concrete coordinator can be sensibly combined with that of the concrete engineer and taken on by an experienced engineering office. The client should therefore assign such a task to this office. Unfortunately, the reality is that a coordinator is not available for most architectural concrete projects which means that there is virtually no expert liaison between planning and execution. As a consequence, this gives rise to well-known problems and differences between the views and expectations of the contractor / architect and those of the construction company particularly with regard to the quality and costs.


PERI – the competent partner in the architectural concrete team

For the selection of the most suitable formwork system and formlining, architects are expertly advised by our specialist engineers. Accompanying detailed solutions are thereby provided which also have an affect on the architectural concrete concepts of the architect.

Consultation

For the selection of the most suitable formwork system and formlining, architects are expertly advised by our specialist engineers. Accompanying detailed solutions are thereby provided which also have an affect on the architectural concrete concepts of the architect.

Construction companies are provided with specialist support for the drafting of formwork offers including during the submission phase.

If the construction company is awarded the contract, we provide an offer which fulfi ls the desired architectural concrete requirements made on the formwork. In the process, we are able to offer cost-effective solutions through the use of system equipment from the rental park which can meet the quality requirements.

In case of order, we provide the complete planning of the formwork for the preassembly as well as the execution on the construction site. If necessary, the planning is supplemented by required assembly drawings and static calculations.

Formwork planning

In case of order, we provide the complete planning of the formwork for the preassembly as well as the execution on the construction site. If necessary, the planning is supplemented by required assembly drawings and static calculations.

Especially with geometrically complicated forms, the demands of the architect can often only be realised with self-compacting or lightly-compacting concrete. The higher fresh concrete pressures that occur here are taken into consideration by the building contractor during the formwork planning according to the specifi cations provided.

In this respect, the revised version of the DIN 18218 provides realistic load assumptions which ensure an economical formwork solution.

In the PERI formwork assembly, the formwork elements are prefabricated according to project specifi cations and in transportable units. If requested, on-time transport to the construction site can also be organised.

Pre-assembly

In the PERI formwork assembly, the formwork elements are prefabricated according to project specifi cations and in transportable units. If requested, on-time transport to the construction site can also be organised.

In order to effi ciently arrange the formwork utilisation from the beginning, construction site personnel are briefed and trained by experienced PERI supervisors.

Construction site support

In order to effi ciently arrange the formwork utilisation from the beginning, construction site personnel are briefed and trained by experienced PERI supervisors.

The proven PERI rental and delivery service is also available for architectural concrete formwork.

Rental and delivery service

The proven PERI rental and delivery service is also available for architectural concrete formwork.

Even the return of materials is handled in a customer-oriented manner. Thus, dismantling and cleaning of the formwork equipment at the PERI logistics centres can be arranged at cost-effective conditions.

Project completion

Even the return of materials is handled in a customer-oriented manner. Thus, dismantling and cleaning of the formwork equipment at the PERI logistics centres can be arranged at cost-effective conditions.

Basic conditions for the planning and execution of architectural concrete components

Basic conditions for the planning and execution of architectural concrete components
Basic conditions for the planning and execution of architectural concrete components

Definition of the 4 architectural concrete classes


AC 1

  • Concrete surfaces with low design requirements e.g. basement walls or areas having a predominantly commercial use

AC 2

  • Concrete surfaces with standard design requirements (e.g. staircase areas, retaining walls)

 

AC 3

  • Concrete surfaces with high design requirements (e.g. Façades in building construction)
     

 

AC 4

  • Concrete surfaces with particularly high design requirements (e.g.: prestigious structural components in building construction)

Formwork-related explanations regarding the criteria: texture, formwork element joints


T1

  • In the formwork element joints, leaking grout/fine mortar up to 20 mm wide and approx. 10 mm deep is permissible.
  • Frame impression of the formwork element permissible.



     

For this requirement, all system formwork which corresponds to the GSV (German Quality Protection Association for Concrete Formwork) "Quality Criteria for Rental Formwork Guideline" is applicable if used correctly. Additional sealing of the formlining and formwork element joints is not necessary. The formlining class is to be assessed separately.







 

T2

  • In the formwork element joints, leaking grout/fine mortar up to 10 mm wide and approx. 5 mm deep is permissible:
  • Element joint off-set up to approx. 5 mm permissible.
  • Height of remaining nibs up to approx. 5 mm permissible.
  • Frame impression of the formwork element permissible.

For this requirement, all system formwork which corresponds to the GSV (German Quality Protection Association for Concrete Formwork) "Quality Criteria for Rental Formwork Guideline" is applicable if used correctly. Particular attention must be paid to ensuring a correct element join in the joints. Additional sealing is not normally necessary. The concrete must possess good water retaining characteristics and is not prone to bleeding. The formlining class is to be assessed separately.



 

T3

  • Smooth, closed and, to a large
    extent, uniform concrete surface.
  • In the formwork element joints, leaking grout/fine mortar up to 3 mm wide permissible.
  • Fine, technically unavoidable nibs up to approx. 3 mm permissible.
  • Other requirements (e.g. tie arrangement, formlining joints, cone seals) are to be specified in detail.

The use of panel formwork is only possible if having a frame impression on the concrete surface has been expressly allowed. With girder formwork, the formlining sheets are pushed directly together. Additional sealing in the element joints using sealing strip or similar material is strongly recommended for T3 but this is dependent, however, on the accuracy of the formlining edges. This work is an additional service and must be agreed upon accordingly together with appropriate compensation. The concrete must possess good water retaining characteristics and is not prone to bleeding. The formlining class is to be assessed separately.

Colour uniformity


If the quality of the formlining is of a good standard, the influence on the colour consistency of the concrete surface is only minimal.

The absorbency of the formlining does have an influence. As the degree of absorbency increases, the colour of the concrete becomes darker. With wood surfaces without any coating, the grain begins to appear due to the different absorbent qualities of early wood and late wood, as well as of cross-grained wood (branches). Sheets with a phenol resin film have very weak absorption characteristics. However, as the number of uses increases, there is a corresponding change in the absorption characteristics so that the concrete surface turns increasingly darker. All-plastic sheets or those with a polypropylene coating do not have any absorption characteristics. As a result, no colour change to the concrete surface – caused by the formlining – occurs with these materials during increased use.

The roughness of the formlining influences the flow behaviour of the ultra-fine concrete particles and water on the formlining surface. Smooth surfaces favour the formation of water streaking effects on the concrete surface. If necessary, the concrete composition is to be changed here. Impurities on the formlining surface can become more firmly fixed due to an adhesive-type release agent, or excessive use of an agent, and lead to a discolouration of the concrete surface.

With increasing requirements on the concrete surface, the formlining is therefore to be carefully cleaned and protected up to the time of concrete placement.

Influence of the release agent: the effects of the release agent on the colour consistency of the concrete surface, see Section 7 (see Best Practice Handbook), "Release Agents".

Evenness


Architectural Concrete

The evenness requirements according to DIN 18202:2013-04, Table 3, Lines 5 and 6 (see Best Practice Handbook), are achievable without any extra effort through appropriate use of formworking materials and maintaining the predetermined fresh concrete pressure.

Higher evenness requirements are to be agreed upon separately. All work required for this is to be specified in detail by the client.

Note:
Higher evenness requirements, e.g. line 7 (see Best Practice Handbook), cannot be technically carried out in an effective manner.

In individual cases, measures are to be determined depending on the selected formwork and formlining systems, as well as the possible tolerances, e.g. for wall formwork

  • due to swelling and shrinkage of the formlining,
  • from the formwork system (production and assembly tolerances),
  • from the tie system (tie expansion),
  • from the measuring system,
  • assembly tolerances on the construction site,
  • reduction of the formlining stiffness due to an increase in the moisture content of the panel and other reasons

determining threshold values or additional measures.

Normally, special demands are placed on the offset at the formlining joint or formwork element joint. For the formlining tolerances (see Best Practice Handbook p. 28).

Construction and formlining joints


AF 1

  • Offset of areas between two concreting sections up to approx. 10 mm permissible.
  • This requirement is achievable with all PERI system formwork if used correctly without any additional measures.

AF 2

  • Offset of areas between two concreting sections up to approx. 10 mm permissible.
  • Leakage of fine mortar onto the previous concreting section must be removed in good time. Trapezoidal strips or similar are recommended.

This requirement is achievable with all PERI system formwork if used correctly. Special attention is to be paid to the contact pressure of the formwork for the second concreting section (e.g. from formwork ties and props) on the first concreting section. Additional sealing strips are not required. Using a trapezoidal strip in the first concreting section results in a sharp-edged, straight joint design.

AF 3

  • Offset of areas between two concrete sections up to approx. 5 mm permissible.
  • Leakage of fine mortar onto the previous concreting section must be removed in good time.
  • Trapezoidal strips or similar are recommended.

This requirement is achievable with all PERI system formwork with careful planning and execution particularly for the second concreting section (props, tie arrangement and tensioning, limiting deflection). Additional sealing strips (e.g. sponge rubber) are recommended. Trapezoidal strips or similar as in AF 2.

AF 4

  • Planning of the detailed execution is required.
  • Offset of areas between two concrete sections up to approx. 5 mm permissible.
  • Leakage of fine mortar onto the previous concreting section must be removed in good time.
  • Other requirements (e.g. design of construction and formlining joints) are to be specified in detail.

On the basis of those requirements specified for the joint, detailed planning is to be provided depending on the selected formwork system and the formlining. In the process, the swelling and shrinking characteristics of the timber material (formlining) in particular are to be taken into consideration.

Porosity


porosity

The porosity of the concrete surface depends on different factors. In Table 2 of the DBV Code of Practice, the number of pores has been evaluated on a test area measuring 0.50 x 0.50 m.

In the process, pores Ø < 2 mm are not taken into account and pores Ø > 15 mm excluded.

Influences from the formlining on the porosity of the concrete surface:

Using vibrated concrete

During concrete compaction on vertical or inclined surfaces, pores filled with water/air and fine particles move towards the formwork surface. On the concrete surface, the proportion of air and water pores increases. With non-absorbent formlining, no water is assimilated from the concrete and the pores are visible on the concrete surface. With an increased absorbency level of the formlining, water from the concrete surface is absorbed by the formlining itself. This means that the amount of water pores on the concrete surface is then reduced.

Roughness of the formlining and adhesiveness of the release agent

Using a smoother type of formlining and a lower level of release agent adhesiveness (very thin film of a quick-drying release agent), means the less the pores attach themselves to the formlining surface and rise more easily. In order to take advantage of this effect, small pouring layer heights (0.30 m to 0.50 m) are to be maintained when concreting and concrete compaction carried out according to DIN 4235-1:1978-12 Part 2 and Part 4, Issue Date 1978-12.

Easy compacting (F5 and F6) and self-compacting concrete (SCC)

Due to the absence of compacting energy through the vibrating process, pores as well as the finest grains do not move to the formwork surface. This means that the proportion of pores on the concrete surface is not increased.

The absorbency of the formlining has the same influence as with vibrated concrete. The influence exerted by the roughness the formlining as well as the adhesiveness of the release agent does not have any measurable significance.

Formlining classes


Formlining class FC 1

Formlining and formwork systems from rental parks which correspond to the "Quality Criteria for Rental Formwork Guideline" issued by the Güteschutzverband Betonschalungen e.V. (German Quality Protection Association for Concrete Formwork), can be used for this formlining class without hesitation.

Formlining Class FC 2

Formlining and formwork systems from rental parks which correspond to the "Quality Criteria for Rental Formwork Guideline" issued by the Güteschutzverband Betonschalungen e.V. (German Quality Protection Association for Concrete Formwork), can be used for this formlining class without hesitation. If necessary, individual elements which have been damaged by an internal vibrator or are badly scratched are to be replaced. For sheets coated with phenol resin, e.g. Fin-Ply, the colour of the concrete can vary due to different utilization rates of the elements.

Formlining Class FC 3

With the use of formwork systems from the rental park, elements with new, undamaged formlining are to be used. When using panel formwork with demands on the texture (Table 2 of the DBV Code of Practice "Architectural Concrete"), it must be checked whether the frame impression of the element can be tolerated. Project-related formwork elements (standard elements or specially-joined panels) consisting of system components with new formlining fulfil Formlining Class 3 requirements if used appropriately.

Note: regarding how long the formlining can be used for the respective architectural concrete surface is to be checked by the contractor each time before further use.

Praxishandbuch - Sichtbeton

Best Practice for Architectural Concrete

More than 100 pages of valuable expert knowledge – concise, instructive and practice-oriented.

 

PERI contacts

Find the right PERI contact for your projects.

Sales contacts worldwide

Send us a message

PERI project examples

Fairfaced concrete has undergone a remarkable change over the past 60 years. Perceived as a synonym for masses of material for often dull megaprojects of high-rise and infrastructure construction over the first 30 to 40 years, its enormous design potential has only become evident over the past two decades. For PERI, too, fairfaced concrete is the most prestigious area of concrete construction. Because it is the litmus test of what can be created in modern construction when everyone involved in the project sees themselves as collective defenders of high-quality architecture. We feel all the more obliged to this since PERI has been chosen to provide the technology and the engineering for a plethora of international fairfaced concrete structures: for high-rises and cultural buildings as well as for traffic route construction.