Sculpting with Reinforced Concrete

Introduction

Many years ago as a carpenter apprentice I was introduced to the different aspects of what carpenters do in construction. They frame houses with wood, build and install cabinets and floors, shore up buildings, drive sheeting to hold back the oceans and earth, install locks and build forms for concrete foundations and buildings. My girlfriend at the time and now my wife of 45 years, whose brother was a carpenter foreman specializing in concrete construction prompted me to find my way as a carpenter specialist in concrete formwork. The work was tough but the overtime pay was good since one never knew when the truck would arrive with the concrete. As many years progressed and I became interested in the fine arts, I asked myself why there were so few concrete works of art. In 1994 I secured the reinforcing steel to begin my sculptures. The steel still remains at the house I sold in 2001. In 2007 I began to create sculptures and realized that this was something I already started 40 years ago.

The world of sculpture includes many media and many styles. Based on a look at Sculpture magazine it would seem that sculpting is dedicated to representing people, flowers, animals and in a few cases abstract ideas. The media used in these depictions may be wood, plastic, stone, metal, glass or some combination of them. Richard Serra uses steel; Louise Nevelson used wood found in the garbage; and Dale Chihuly uses glass. Historically it is hardly ever the case that reinforced concrete is the medium of a sculpture. However, over the last 30 years the use of this medium has increased.

What is Reinforced Concrete?

We have all seen the large trucks with mixing barrels rolling down the streets bringing what most people would think of as cement deliveries to various construction sites. There is cement in the truck barrels but it is being mixed with sand, water and various sized stones to create a medium called concrete. Concrete is used on construction sites as foundation materials and as the skeleton of various buildings, dams, bridges and tunnels. Concrete is an exceptionally strong material but what makes concrete even stronger is the addition of a steel framework or structure as reinforcement. Adding steel to the mix of concrete prevents 70-story buildings from crashing to the ground. Concrete is strong under compression but the forces of weight pushing and pulling the concrete requires the addition of reinforcing ridged steel pieces preventing movement and potential cracking. Note the reinforcing cage below and the reinforcing steel with continuous ridges throughout. Each ridge in the steel keeps the concrete in place. The reinforcing steel, also known as rebar would not work if the bars were smooth. Cracking of the concrete mass may be a sign of a significant weakening of the structure. The failure to install appropriate reinforcing steel into the concrete mix will set the stage for a work heading for collapse.

Reinforced Concrete Environments

Reinforced concrete unlike other sculptural media may be used for both interior or exterior art. It is immune to the weathermaking it ideal for outdoor use, but may also stand indoors. Concrete works may be as small as ashtrays or as large as private homes. In small structures instead of half inch reinforcing bars forming the work, various sizes of steel mesh can be used for the structural steel part of the concrete work. Some concrete works may be functional like the table below; others provide simply aesthetic pleasure. Some are also representational and others are abstract. Some consist of reinforced concrete alone and others are a combination of concrete and other media as well.

Samples of Reinforced Concrete Sculptures

Processes of Concrete Sculpting

Concrete works may be manufactured horizontally, vertically or by a building-up process. In the building-up process one adds masses of concrete slowly as the liquid concrete on the bottom sets to allow the top portions to be added. Usually the building-up process is used for a work in which unusual shapes are the desired end product. For example creating a concrete horse or tiger would be done with a building-up of the concrete mass and shaping parts of the mass to a design. Horizontally a flat platform form is laid on the ground and wood sides are attached to the platform to create the outline of the work to be created. Using wood to create the outline or shape of a concrete product is known as forming the product. The wood is the form and the process is forming. When the work has reached its ultimate hardness it is said to have cured. Curing is the chemical process whereby the liquid of concrete turns into a solid with a given strength. Cured, the work is stood up and set into a concrete footing for stability. In the vertical approach a footing is constructed and the form is set on the footing outlining the work and the concrete is poured into the vertical form. Size counts utilized this method. Concrete may be used as the foundation of the work and/or the work itself.

A significant problem for the sculptor using a horizontal process is lifting the finished product. Reinforced concrete is a heavy product. This problem can be corrected by using admixtures other than stone. Plastics, gases, and fly ash or any of a number of substances may be used to reduce the weight to be lifted. The substituted mixtures must be evaluated in terms of strength and curing time. Substituted mixes may reduce strength and increase curing time.

Reinforced Concrete and the Elements

Besides reinforcing steel the strength of concrete is determined by the ratio of the mix of cement to sand and stone aggregate, the amount of water and the temperature at which it is allowed to set. Concrete strength results from the addition or subtraction of cement to the mix. The higher the proportion of cement the greater the strength. The more water added to the mix the weaker the concrete will be after it has set. Since water is necessary to the mix of the concrete the final strength is also affected by temperature. Concrete does not set as hard in cold weather and as such the conditions for pouring concrete must be controlled such as applying heat or covers to maintain a temperature above freezing. If concrete freezes before it has set it is worthless. It has no strength and will disintegrate as time goes on. The sign that concrete has not set properly is that after 24 hours it is green rather than gray in color. Excessive temperatures create problems for concrete in that as heat evaporates the water in the concrete mix too quickly the concrete will not congeal and shrinkage cracks will result. Concrete is a mixed product moving ultimately through a chemical process to a hardened state. Working with concrete requires that one be vigilant of its finishing window. As it hardens it becomes more difficult to work with it. It is virtually impossible to come back after the concrete has set and try to complete the final appearance – it must be worked while it is setting. Although grinding is not practical for hardened concrete, it is available as a tool to smooth rough protrusions.

Benefits of Reinforced Concrete

The most significant benefit of reinforced concrete is its strength. It can withstand great weights above it and weights pushing out from it. The strength to hold objects together allows the sculptor tremendous flexibility in moving outside the plane of the foundation. Daniel Lebeskind’s Denver Museum addition used a massive reinforced concrete footing to carry the weight of the outward point of the building. The holding strength or attachment capabilities of concrete require steel supplements such as anchor bolts embedded into the concrete mass which allow a connection to other materials. Empty Head is a reinforced concrete mass which contains connections to metal pipes via threaded rods. The ability of reinforced concrete to allow other media to be added on via connections makes for great flexibility in the work being created. Reinforced concrete is also compatible with a myriad of materials that can be used in combination with it. Wood, steel, glass, metal, all can be combined with the concrete. In addition to strength, flexibility, compatibility, concrete is long lasting, requires little maintenance and can be colored with the addition of various dyes. Although concrete becomes increasingly stronger as time goes on, it can be changed with the use of various cutting and grinding tools. Like a piece of granite it can be chipped, cut and ground smooth if the end result does not match the original concept.

Yes, reinforced concrete in its cured form is a difficult medium to use for sculpture productions. Grinding and chipping away concrete to create a work is a time consuming and dirty job. In its liquid form it allows the sculptor as much freedom to manipulate his creation as if he was using clay. Concrete is however, much stronger, more durable and amenable to the addition and attachment of other media than clay, allowing the sculptor greater creativity and flexibility.

A second article will be forthcoming dealing with the actual making of concrete sculptures.

— by John Daab Ph.D.  |  December 29, 2008  |  Print Version - PDF

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