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A short class with Sarah and her students. The other ways are under More.
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Today we’re going to discuss deleterious substances in aggregates, which can negatively impact our concrete. What do you think 'deleterious' means in this context?
Does it mean harmful or bad things in the aggregates?
Exactly! A good way to remember this is through the acronym 'DANGERS' - Detrimental, Altering, Noxious, Grading, Enhancing, Reducing Strength. These substances weaken the concrete itself. Can anyone name some examples?
Is clay one of them? I remember it weakens the bond.
Correct, clay is a significant deleterious material. Let’s summarize: clay and silt, for instance, can increase water demand and weaken the bond with cement.
Now that we know what deleterious materials are, let's talk about how they affect concrete. What effect do you think organic impurities have?
I think they might slow down how fast the concrete sets up?
Right! They can actually retard setting and hardening. Remember the phrase 'organic is slow'? That might help you recall its impact.
What about salts? I heard they can cause problems too.
Yes! Salts can lead to corrosion of steel and efflorescence. Think of 'salties corrode!'. It’s crucial to monitor these materials to maintain concrete durability.
Let’s shift focus to permissible limits for these troubling materials. Who knows what the limit is for clay lumps?
Is it less than 1%?
Perfect! Just like '1 is number one, keep clay lumps under'. Let's continue – what about soft particles?
Oh! That should be less than 3%. I remember because three is a few.
Excellent memory! Monitoring these limits helps ensure concrete can withstand the test of time.
Clay in aggregates increases the water required for a mix by 20% at times, affecting the water-cement ratio.
Presence of organic impurities can delay concrete setting for hours, leading to project delays.
Salts in aggregates have been linked to premature concrete spalling due to efflorescence.
Clay is gray, it takes away; water rushes needed each day.
A builder learned that clay made his mortar weak, and that salty roads caused terrible streaks. He mixed wisely, avoiding the wrong things, and strengthened the concrete for good functioning.
Remember C.O.C.S. - Clay, Organic, Coal, Salts.
DEAL - Deleterious effects include: Increased water demand, Enhanced setting time issues, Loss of strength.
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What negatively impacts concrete performance?
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What is the permissible limit for clay lumps?
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How do organic impurities affect concrete?
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What do salts cause in concrete?
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Substances that negatively affect the performance and durability of concrete.
Fine-grained soil that weakens the bond with cement and increases water demand.
Substances derived from living organisms that can retard the setting and hardening of concrete.
Substances such as chlorides and sulfates that can lead to corrosion and efflorescence.
The maximum allowable percentage of deleterious materials in concrete aggregates according to industry standards.
Deleterious substances in aggregates can significantly hinder concrete performance by affecting strength, setting time, and durability.
This section identifies various deleterious materials such as clay, organic impurities, and reactants that can negatively impact concrete. It also specifies the allowable limits for these materials in aggregates according to industry standards, emphasizing the importance of quality control in concrete production.
Deleterious materials present in aggregates can adversely affect the performance and durability of concrete. Their presence can weaken the bond between cement and aggregate, increase water demand, and compromise the overall structural integrity of concrete mixes.
This section emphasizes the significance of monitoring and controlling the quality of aggregates to ensure lasting performance and safety in concrete structures.