Special Concretes: Types, Uses and Cement Choice — The Complete Guide

A special concrete is not a “better” concrete: it is a concrete in which one specific property has been deliberately pushed — weight, permeability, placeability, strength or durability. You lighten a roof, you drain a car park, you fill a narrow wall, you gain metres of span: every situation has its concrete. This guide tours the families you actually meet on Moroccan sites, from those you can order today to those still living in laboratories, and tells you at each step which cement carries them best.

The families, in one table

The first four families each have their detailed article on this blog — the lightweight guide, the cellular guide, the pumping guide and the HPC guide — this page deliberately stays the overview that helps you choose, then dig deeper.

Lightweight and cellular: the weight family

Ordinary concrete weighs about 2,400 kg/m3. Two routes bring it down: replace heavy aggregates with lightweight ones (expanded clay, pozzolan, slag) — you stay between 1,400 and 1,900 kg/m3 with strengths usable in structure; or create bubbles in the paste (foamed concrete, cellular concrete), dropping to 400-1,600 kg/m3 for filling and partitions. The choice follows the allowable load of the support: you do not lighten on principle, you lighten because an old floor, a frame or an overload rule demands it. What never changes: a monitored water/cement ratio, careful curing, and lightweight aggregates pre-soaked before mixing — they drink the mixing water otherwise, and setting drifts.

Pervious concrete: let the water through

Pervious (or porous) concrete cuts back fines to create 15-25% connected voids: rain crosses the slab instead of ponding and running off. It is the natural answer for yards, driveways, light car parks and footpaths in the South, where brutal showers turn sealed surfaces into mirrors. Three success conditions: a draining base layer of crushed stone genuinely designed to evacuate (otherwise the water crosses the slab and sits underneath), deliberately limited fines, and accepted maintenance — permeability drops as voids clog, and periodic pressure washing restarts the performance. Target strength stays modest (a pervious slab does not carry industrial traffic), which makes CPJ 45 largely sufficient.

Pumped concrete: the mix travels

Pumping means sending concrete through a pipe — and concrete only travels well if designed for it: enough fines, calibrated slump, dosed superplasticiser. It is the daily routine of urban sites without direct access, wide floor pours and upper floors. The full guide covers machines, distances and site rules; the essentials here: pumping is prepared the day before (pour plan, pump position, trial mix), and a concrete that blocks a line stops the whole site. For the cement class, the strength target decides: CPJ 45 for everyday work, CPJ 55 when the mix aims for more MPa.

Self-compacting concrete: pour without vibrating

SCC carries enough fines and high-range superplasticiser to flow into formwork under its own weight, wrapping the densest rebar without vibration — no poker, no noise, no forgotten vibrator. Flow is checked on a flow table (usual classes run from 550 to 850 mm), and stability is checked by eye: an SCC that segregates at the bottom of the wall (paste low, aggregates high) is a badly designed SCC. Its playing field: thin heavily-reinforced walls, shaped architectural pieces, refurbishments where vibration is banned. Its price: a clearly higher cost, justified when labour or access is missing — not for an everyday slab. On class: CPJ 55, for its consistency and fines, is the formulator's natural pick.

Concreting in cold weather: setting on hold

Below 5 °C, the cement reaction slows sharply: the concrete takes days to harden, and early freezing can permanently ruin the final strength. The reflexes: warm mixing water rather than frozen aggregates, a chloride-free set accelerator whenever steel is present, surface protection (sheets, mats) and extended curing until the concrete reaches enough young strength. Nor do you pour straight into a cold snap without an adapted striking plan. In Dakhla the issue is inverted — heat rules — and the hot-weather concreting guide covers that side, with the anti-evaporation curing that goes with it.

Porosity: the hidden parameter of durability

Every attack on concrete — frost, chlorides, CO2, sulfates — travels through its pores. And capillary porosity depends directly on the water/cement ratio: more water, more connected capillaries, more doors for aggressions. That is why the W/C ≤ 0.50 rule returns in every guide of this series, and why curing counts as much as batching: properly hydrating the cement closes porosity. A well-designed special concrete does not escape this physics: an HPC owes its relative immunity to its refined porosity, and a badly cured lightweight cracks precisely because its paste, more solicited, dries too fast. The articles on cracking and on chlorides detail these mechanisms.

The concretes of the future: promises and realities

Now to the headline families — and let us separate what exists from what is brewing. Geopolymers activate industrial by-products (slags, pozzolans) without clinker: the CO2 footprint drops sharply, industrial floors and precast elements exist abroad, but there is no harmonised product standard equivalent to the NM 10.1.004 / EN 197-1 that governs ordinary cements — so no standardised delivery nor established contractual frame in Morocco today. 3D printing extrudes mortars layer by layer: decorative walls, street furniture and architectural prototypes are being built, but rebar — the skeleton of reinforced concrete — remains the lock. Nanotechnologies (nano-silica first) already slip into modern HPC to refine the microstructure: the quietest and the most genuinely in-service family. Bacterial concrete precipitates limestone inside micro-cracks thanks to dormant bacteria: spectacular, proven on pilots, still far from site pricing. Translucent concrete embeds optical fibres in the matrix: an architect's signature, not a catalogue product.

What these families share: none is a routine product in Morocco today. We follow them — our trade is precisely knowing when a technique leaves the lab for the site — but we prefer to tell you where reality stands rather than sell you the future.

Which cement for which special concrete

In every case, batch consistency counts as much as class: a special concrete is a hair-tuned formula, and a cement that drifts between deliveries sends slump, setting time and strengths wandering. That is exactly what a modern plant with its per-batch certificate masters.

What DAM produces — and does not

We produce grey CPJ 45 and CPJ 55, compliant with NM 10.1.004, delivered in Dakhla and the region, with a certificate per batch. We neither formulate nor sell ready-mixed special concretes, admixtures or lightweight aggregates: these concretes are designed with your plant, your formulator or your mason, who buy their additions and admixtures from specialised suppliers. Our role — the purpose of this guide — is to supply the consistent, documented binder these formulas are built on, and to let you talk to those intermediaries from knowledge.

In summary

A special concrete = one property pushed to the max, a cement that still conducts the orchestra, and increased execution discipline: lightweight or cellular for weight, pervious for water, pumped for access, self-compacting for impossible formwork, HPC for performance — and for the future, promising families not yet orderable as standard. Cement choice follows a simple thread: CPJ 45 until proven otherwise, CPJ 55 as soon as the mix's strength or consistency justifies it — always validated by a trial mix before the pour.