Concrete comes in different grades or strengths. Normally the engineer specifies the design strength of the concrete, which may vary for different parts of the building. Using concrete which is under strength will lead to problems with the structure, which could cause cracking and in the worst case catastrophic failure of the building. Using concrete of a higher strength or grade than required is more expensive.
Concrete can be mixed on the building site, usually using a mechanical mixer. or it's ordered from a ready mix concrete supplier which delivers the concrete in concrete spinner/ready-mix trucks with revolving drums which continually mix the concrete. When ordering concrete it's important to specify the grade or strength and the amount of concrete required.
Concrete is a mixture of cement, water, sand and stone. The strength of concrete depends on the ratio of cement to water. The more cement the stronger the concrete, while the more water the weaker the concrete. More water usually also means that the concrete shrinks more as it dries, which usually causes shrinkage cracks that are unsightly and which allows moisture to penetrate the concrete.
Adding stone reduces the amount of water. But too much stone means that the concrete will be difficult to work with and there will be voids between the stones. It’s important to note that the stone should be clean and free of dust and dirt, since the dust and dirt will require more water, which will make for a weaker concrete unless more cement is added. Stone should be generally of a uniform size.
Sand helps create the cement paste that fills the voids between the stones. Sand should be clean and free of contaminants, such as roots, sticks, rubbish and impurities. Not all sand is suitable for concrete. The best sand is a river sand which is of even grading. Sand which is too fine will require more water to wet it, and as already discussed more water means more cement or a weaker concrete. When the sand is very course the concrete may have voids, or be difficult to compact. If the sand is very wet then less water should be added to the mixture. Where possible sand for concrete should be kept dry and covered when there’s lots of rain.
Sometimes, depending on the available sands and stone it may be necessary to blend two sands together.
Sand, water, cement and stone must be well mixed so that the cement is evenly spread through the mixture and there are no lumps of material. The mixture is now known as concrete.
Concrete usually begins to set within four hours of being mixed. The time will be shorter when it’s very hot. The setting time will be extended when it’s cold, or when retarders (certain chemicals) are added. In fact, add sugar and the concrete will never set. So concrete should be placed and compacted as soon as possible. When concreting bigger structures it’s important to ensure that the first concrete placed doesn’t dry out before the next load of fresh concrete is added next to it. So it’s good practice when pouring slabs and beams to start pouring from one side of the structure, first bringing the concrete to the top surface, then steadily advancing with each new load of concrete, ensuring that the fresh concrete knits with the older concrete. If the new concrete is placed against older concrete that has already started to set it won’t join properly and there’ll be a ‘cold joint’ (visible joint) which is unsightly and weakens the structure, even meaning that the structure is unsuitable and should be condemned. It’s therefore critical to schedule concrete deliveries at the correct frequencies, so that there isn’t a long gap between trucks and also so that trucks are not standing, waiting for previous trucks to be offloaded, meaning that the concrete is already starting to set. You must place the concrete at a fast enough rate so that the concrete doesn’t start setting before fresh concrete is added.
Concrete is best compacted by mechanical vibrators, or compactors, to ensure there’re no voids in the structure and to bring some of the concrete water to the surface. Concrete shouldn’t be over compacted.
The concrete mixture should always be workable, having sufficient water, cement and sand so that it can easily flow into voids, between and around reinforcing steel, and so it can be readily compacted and worked with. However, construction crews should never add additional water to the concrete mix to make it more workable. Remember the golden rule, more water equals weaker concrete! Only the mixing crew should add more water, plus the required additional cement.
As the concrete starts to set the top surface should be finished and smoothed off. The final finish will depend on what will come on top of the concrete. Floors that will have a carpet or vinyl floor finish will be required to have a smooth (‘steel float’) finish. Floors that will be covered with tiles may only require a rougher finish. However, in all cases it’s important to ensure that the top surface of the concrete is finished to the correct required levels without dips and humps. A smoother finish takes longer, so can be more expensive. A very smooth finish could be unsuitable when other layers are added, say when a screed is to be placed over the concrete.
Protecting Your Newly Laid Concrete
Concrete shouldn’t be allowed to dry out too quickly which will cause shrinkage cracks and slow down the strength gain. Fresh concrete should be cured for seven days so that it retains moisture. This curing should start as soon as it has been worked smooth and set. Curing of concrete can be done by:
Conclusion - Ensuring your Concrete Building Structure is Sound
It's important that those working with concrete ensure that the correct grade of concrete is used. As soon as the concrete is mixed, or it's delivered to the project, it should be poured or placed into the structure. Concrete that's too dry or that has too much stone is difficult to work with and won't always get into all the corners and around the reinforcing in the structure. Concrete that's too wet will often have excessive cracks in it when it dries.
Care should be taken not to add additional water to the wet concrete since this weakens the concrete. Adding additional water usually means you should also add more cement.
Concrete must be thoroughly compacted and care must be taken to ensure it's finished to the correct level and worked smooth.
Using the wrong grade of concrete, adding additional water, using unsuitable sands or contaminated materials, not compacting the concrete correctly, allowing the concrete to set before the next batch of concrete is added, or failing to cure the concrete correctly, could result in excessive cracking and a weakened structure which will cause problems for your new house.
For more valuable tips and advice read: 'An Introduction to Building and Renovating Houses - Volume 1 Hiring Contractors, Managing Construction and Finishing Your Home' and'Volume 2 Finding Your Ideal Property and Designing Your Dream Home'
This is an extract from: 'An Introduction to Building and Renovating Houses Volume 1' by Paul Netscher. Available in paper or eBook from Amazon.com, Amazon UK, Amazon CA, Amazon AU and all online bookstores. To read more
© 2019 This article is not to be reproduced for commercial purposes without written permission from the author.
8/12/2020 04:03:07 am
So well written. Concrete is quite the trade to be in! Skilled contractors can always indulge in learning new up to date ways!
31/12/2020 05:14:20 pm
Thanks for having this article, it helps a lot. It’s a well-written blog and it is very informative. Keep on blogging, looking forward to see more of your posts!
22/1/2021 09:39:20 pm
Thank you for sharing such informative article! We are just wondering how to find a good contractor to help us with the concrete foundation for our new house ! Pretty sure that we will begin our search for any contractor near our house and look at the online reviews and testimonials! We just think they do know their stuffs, the characteristics of soil and local regulations, references etc. We 'd love read and respect other feeling in any review, anyway, we also would like to look at their reference projects nearby our house in Marion! Regards, Malcolm
24/2/2021 11:38:43 pm
It really helped when you talked about the importance of getting a concrete job done right. My wife and I want to start building our dream house, and we decided that we want to have a basement on it. We want to make it into a cool home theater space, so we need to find a concrete contractor for the job. We really appreciate your information about concrete. I'm sure it'll help us know if a concrete contractor's right for the job or not.
3/3/2021 11:12:20 am
You made a good point when you shared that it's necessary to specify the grade and the amount of concrete required when you are ordering from a supplier. In this way, you will acquire the one that has good quality for your project. I would like to think if someone is working on a construction project, he should consider getting the right concrete from a reliable supplier.
24/5/2021 07:31:37 pm
To be honest, it's new to me that concrete also depends on weather to set.
25/5/2021 05:44:25 pm
I always like this type of post! Thank you for sharing your knowledge about fly ash. Your content is so informative and awesome. Keep Sharing!!
25/5/2021 06:05:03 pm
Great post! Thank you for telling me that a contractor with the most years of experience is more likely to do a better job with the foundation and other aspects of construction.
25/5/2021 06:13:48 pm
Awesome article! Thank you for sharing your idea! We are a new concrete company, Your info really hits important points. Communication is key in any business or trade. Thanks!
8/7/2021 10:40:45 pm
I’m not that much of a internet reader to be honest but your blogs really nice, keep it up! I’ll go ahead and bookmark your website to come back down the road. We are also offering similar Services.
13/8/2021 05:46:30 pm
Nice Blog!! The content you have shared is very elaborative and informative. Thanks a lot for sharing such a great piece of knowledge with us.
7/10/2021 07:42:22 pm
Nice Article...Very interesting to read this article. I have learned some new information. Thanks for sharing.
19/10/2021 06:20:19 pm
Excellent post! I agree that the contractor with the most years of experience is more likely to perform better on the foundation and other aspects of construction.
17/11/2021 02:43:48 pm
I do appreciate that this post stressed on the importance of proper concrete maintenance as it helps to extend its longevity and usability. My wife and I sre planning to have our concrete driveway repaved. I will look for an experienced contractor to help us.
27/1/2022 04:08:55 am
A big part of understanding concrete strength is understanding the different types of forces or stresses placed on a slab of concrete. Thank you for the beautiful post!
29/1/2022 05:24:28 am
The more cement the stronger the concrete, while the more water the weaker the concrete. Thank you for the beautiful post!
28/2/2022 05:13:38 am
It’s important to note that the stone should be clean and free of dust and dirt, since the dust and dirt will require more water, Thank you for the beautiful post!
22/4/2022 05:18:02 am
The concrete shrinks more as it dries, which usually causes shrinkage cracks that are unsightly and which allows moisture to penetrate the concrete, Thank you for making this such an awesome post!
4/7/2022 08:40:28 pm
Hi, after reading this awesome piece of writing I am too glad to share my knowledge here with colleagues.
9/7/2022 03:10:26 am
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I never took into account the fact that concrete will crack and shrink when they drys out quickly. With that in mind, it would be a good idea to let the professionals do the process for me and just order a concrete delivery instead. It will ensure that the process is done right and the material will definitely last for a long time without any issues.
6/8/2022 01:41:29 pm
I like the tip that you gave that you could mix your concrete on the worksite if your contractor wanted. The other night, my friend informed me that he was looking for ready mix concrete for faster production for his residential project, and he asked if I had any idea what would be the best option. I appreciate this instructive article, I'll tell him that it will be much better if they consult trusted concrete services as they can provide more information about their services.
18/8/2022 06:42:54 pm
Thank you for sharing this informative article about cement and concrete repair. I hope there are a lot of contractors who could read this and be guided accordingly.
17/9/2022 01:11:14 am
Great article! This is going to make the people more curious about what other things they could do with stamped concrete.
17/9/2022 02:24:39 pm
Nice article! This is really great for the people that wants to hire a tree services for the first time.
26/10/2022 06:29:08 pm
Thanks for pointing out that we need to specify what kind of grade or strength is needed when ordering from concreters. I will keep that in mind because I would want a driveway installed this year. It is badly needed to keep our car from getting stuck in then dirt when the ground is wet after it just rained and we needed to go out.
1/11/2022 10:14:29 pm
I want to make sure that I get my driveway installed properly, but I'm not sure how to put it together. It makes sense that working with a concrete specialist would be a good idea. That seems like a good way to ensure that I handle things correctly.
14/12/2022 03:59:43 am
The more cement the stronger the concrete, while the more water the weaker the concrete. More water usually also means that the concrete shrinks more as it dries, Thank you, amazing post!
28/12/2022 04:48:42 am
I didn't know that you needed to wrap the concrete in a plastic membrane. My garage floor needs some major repairs. I'll have to hire a contractor to fill in the mini potholes I have.
29/12/2022 05:25:32 am
More water usually also means that the concrete shrinks more as it dries, which usually causes shrinkage cracks that are unsightly and which allows moisture to penetrate the concrete. Thank you for the beautiful post!
12/1/2023 07:29:48 pm
I'm glad you talked that you could ask your service provider for the supplies of sand for your construction project. My brother informed me yesterday that he was hoping to find a sand supply hauling services that could provide sand delivery for his landscape remodeling project. He asked if I had thoughts on the best option to consider. I appreciate this helpful article, I'll tell him it will be much better if he consults trusted sand supply services as they can answer all his inquiries.
21/1/2023 10:02:57 am
A lot of "experts" don't know the basics, I'll save this one!
25/1/2023 08:08:05 am
My old boss always blamed cracks on the customers, he needs to read this!
28/1/2023 01:58:21 pm
You made an excellent point that one of the benefits of working with an experienced concrete contractor is that they are skilled at ensuring our concrete is built safely and accurately. I am in need of new concrete decorative items installed for my home. I will look at hiring skilled professionals to help get the work done.
16/3/2023 04:20:17 am
20/3/2023 03:32:10 pm
I liked how this post shared that additional water to the wet concrete can weaken it. My friend told me that their project involves concrete leveling. I should advise him to work with a concrete leveling service to ensure precise work.
22/3/2023 01:05:28 pm
Of course it is very important for builders to know more about concrete that is why I am happy that this blog explain a really good details about it. I really appreciated it thank you.
22/3/2023 01:08:04 pm
Knowing more about concrete is really the most especially to us concreters, I am proud that this blog delivered the details well, keep it up for good!
22/3/2023 01:54:37 pm
Very interesting article and informative as well. i have lots of pic on my side and gonna apply it thanks.
22/3/2023 02:08:40 pm
During the building of a structure, concrete is utilized to give strength, durability, and versatility. Due to its exceptional qualities, concrete is a dependable and long-lasting material choice for both commercial and residential structures.
23/3/2023 10:49:27 am
Thank you for pointing out that the proportion of cement to water determines the strength of concrete. My mother wants to construct a home. I'll advise her to hire concrete professionals so that her foundation will be strong.
8/5/2023 08:16:50 pm
Great post on home improvement! Your tips on making small changes and mentioning the importance of maintaining your roof are spot on. I recently replaced my own roof and it made a huge difference in the appearance and functionality of my home. Thanks for sharing your insights.
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I’m a construction professional, author of several successful construction management books, and a home owner. I’ve made mistakes in construction management, I’ve seen others make mistakes, but importantly I’ve had multiple successful construction projects and I’ve learned from the mistakes. I want to share these lessons and my knowledge with you.
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