The Process of Creating a Concrete Sidewalk

Chris Lazration

March 27, 2014

Audience & Description of Scope:

The purpose of this process description document is to present the reader with the basic

knowledge and know how behind the making of a simple concrete sidewalk slab. This document

will begin by focusing on the primary ingredients that make up a concrete sidewalk, and then

will shift into the process of mixing the concrete ingredients and pouring the mixture into a

sidewalk. Upon completion of reading this document, a user shall be able to understand what

ingredients go into a concrete sidewalk, and the process of how those numerous ingredients end

up as a concrete sidewalk slab.

The intended audience for this document is students and/ or any other persons who have

an interest in creating their own concrete sidewalk, but has limited previous knowledge of the

topic. This document would work well in introductory concrete textbooks, as an article in a

simple do-it-yourself book, or even stand alone as a technical process description paper. Due to

the fact that the user of this document has little previous knowledge about concrete sidewalks

and their ingredients, this document should be used as a stepping stone into more in depth,

detailed documents. This document allows the users to grasp the idea of a concrete sidewalk and

its ingredients, but is not too technically based that the user will not understand.

Ingredients of a Concrete Sidewalk:

The evolution of the sidewalk has changed drastically throughout the developmental times

that humans have been carving their marks into this world. From dirt and gravel sidewalks to

more elaborate sidewalks such as concrete, bricks, or stones; today’s sidewalks are made up of

an elaborate mixture of ingredients. Before the process of how a concrete sidewalk is developed,

it is important to thoroughly understand the particular ingredients that make up a concrete

sidewalk. The following list shows the fundamental ingredients and explains their significance

and role in the concrete sidewalk.

1. Water:

Water, by far, is the most important ingredient in a batch of concrete. Without this

ingredient, the mixture would basically just be gravel and some powder; something that is

not hard and not very strong. When water is added to the mixture, it hydrates (causes a

chemical reaction to induce the solidification process) with the Portland cement. This

hydration process bonds together all of the concrete constituents into a robust stone like

materiel, and the process where the concrete receives the majority of its strength.

2. Portland cement:

Portland cement is an ingredient that is generated from grinding a Portland cement

clinker (item that is produced when ground limestone and clay are heated in a kiln),

calcium sulfate, and other constituents into a fine powder; which can be seen below in

Figure 1. This fine powder that is produced is the one of the most important ingredients

in a batch of concrete because it is what actually hydrates with the water to cause

solidification between the concrete constituents.

1Figure 1: Portland cement powder

1 http://www.nachi.org/constituent-materials-concrete.htm

3. Course/Fine Aggregates

In a batch of concrete, the course and fine aggregates typically account for 60-75% of the

total volume of the concrete mixture. These aggregates also strongly influence the

concrete’s hardening properties both during mixing and setting. For example, having both

coarse and fine aggregates allows minimal volume between the actual aggregates; thus

causing the concrete mixture to have a greater strength. In a typical batch of concrete, the

course aggregates (particles greater than 3/8” in diameter) are made up of gravels and

crushed stones; whereas the fine aggregates (particles less than 3/8” in diameter) are

made up of sand particles or really small particles of crushed stone. Figure 2 below

depicts the realm of aggregates.

2Figure 2: Examples of course and fine aggregates

4. Steel Reinforcement:

This is the only item on the list of ingredients for a concrete sidewalk that is not

completely necessary to include. Also, this ingredient does not go directly into the

mixture of concrete; it is pre-placed in the form work and the concrete mixture is poured

over it. Concrete is a material that is very strong under compression, but very weak in

tension. To account for this weakness in tension, steel reinforcing bars are placed in the

section of the slab that would be in tension as depicted in Figure 3 on the beginning of the

next page. Typical concrete items that must include steel reinforcing to prevent failure are

items such as beams, columns, floor slabs, and foundations. It is essential for these items

to include the steel reinforcing because of the huge amounts of loads that they carry; thus

preventing failure. For a typical concrete sidewalk, the loadings do not impose enough

stress on the concrete to cause failure; therefore steel reinforcement is generally excluded

from concrete sidewalks.

2 http://www.statetestingllc.com/aggregate-inspections.aspx

3Figure 3: Depicting how a concrete slab reacts to loading

Mixing Process:

The mixing stage of creating a concrete sidewalk is where all of the above mentioned

ingredients are combined together to get the mixture that will be ultimately poured into the pre-

laid out sidewalk formwork. This mixing of the concrete ingredients can be done in two main

ways. The first way is to combine the ingredients into a container such as a wheelbarrow and to

do the mixing aspect of it by hand. The second way to combine the ingredients is to place them

into a portable concrete mixer, as seen in Figure 4. Once turned on, the mixer will begin to rotate

and will mix the ingredients for the user. The list of steps for adding the ingredients to be mixed

is as follows:

Step 1: Preparing the Dry Ingredients:

1-1 Adding the Portland Cement Powder:

No matter which method of mixing the ingredients was chosen, either by hand or

by mixer, the first thing that needs to be added is the Portland cement powder.

Like stated in the ingredients section, the Portland cement powder is one of the

most important items in a concrete mix, so it is very important to not forget this

powder.

1-2 Adding the Course and Fine Aggregates:

The next ingredients to be added into the mixture are the aggregates. For the

cement batch to turn out correctly, it is important to include the proper aggregates.

In a proper batch, it is necessary to make sure that there are more fine aggregates

than the amount of Portland cement powder. Also, for the batch to turn out

correctly, the amount of course aggregates needs to be more than the fine

aggregates. Typical concrete batches have about a 2:1 ratio of course to fine

aggregates.

3 http://helid.digicollection.org/en/d/Jh0210e/3.3.3.html

1-3 Mixing the Dry Ingredients:

The Portland cement powder, course aggregates, and fine aggregates need to be

thoroughly mixed together before water is added to the mixture to achieve proper

strength in the final concrete. If these materials are not thoroughly mixed together,

the final concrete sidewalk slab will contain air pockets and clusters of

aggregates; both of which make the concrete mix much more susceptible to

failure than if they were properly mixed.

Step 2: Adding the Most Important Ingredient:

2-1 Adding Water:

While the dry ingredients are spinning in the mixer, water is now added into the

mixture. The water causes a chemical reaction with the Portland cement powder

and begins to solidify into a binding agent. This binding agent begins to adhere to

both the course and fine aggregates, and once this mixture is placed into the

forms, the binding agent begins to harden significantly; and the excess water

begins to rise to the surface. When properly done so, the dried, binding agent is

ultimately where the concrete gets its strength from. If this part of the mixing is

not completed properly, the strength of the concrete will be compromised and the

concrete sidewalk will be very vulnerable to cracking and failure.

4Figure 4: Example of a portable concrete mixer

Step 3: Placing the Finished Mix:

3-1 Pouring the Mix:

Once the proper consistency is reached within the mixer, the batch of mixed

ingredients is ready to be placed into the pre-placed form work. The batch is

typically poured from one end of the form work, typically the far end, back to the

4 http://www.hometips.com/diy-how-to/concrete-cement-mixing.html

other end. Once poured, it is essential that the mixture is worked and compacted

thoroughly to ensure that the final slab will not include any air pockets. After the

mixture is worked and compacted, it should be leveled with a tool known as a

screed, and should have time to settle and hydrate before anything else is done to

it. Right before the concrete mixture hardens and is still workable, the concrete

sidewalk slab should be trialed over with a tool known as a bull float. This tool is

used to finish the surface of the concrete by smoothing out the imperfections.

These tools and a finished concrete slab can be seen in figure 5.

5Figure 5: Top Left, an example of a creed 6Bottom Left, an example of a bull float

7Right, an example of a finished concrete sidewalk still in the formwork

Conclusion:

Overall, the process and the items that make up a concrete sidewalk are pretty basic and

trivial. With some simplistic ingredient definitions, and a vague overview of the mixing and

pouring process, one should now know the basic principles behind the construction of a concrete

sidewalk. With that being said, these basic principles set the user up for a successful trail at

constructing their own concrete sidewalk. These principles may also lead them to a more detailed

analysis of the particular part of the process that they would like to learn more about before

tackling a concrete sidewalk project. Either way, this document gets the users brain stirring about

how to construct a concrete sidewalk.

5 http://www.altaviewconcrete.com/the-perfect-pour

6 http://www.altaviewconcrete.com/the-perfect-pour

7 http://www.pacificgroupdevelopments.com/services/concrete-forming-finishing